With the free version under Mac OS X, click on the application icon of Sweet Home 3D while maintaining the ctrl key pressed to display its contextual menu, choose Show Package Contents item, open the Contents folder, edit the Info.plist file by dragging its icon on TextEdit application and update the maximum memory in the text <string>-Xmx1024m</string>, writing for example <string>-Xmx2g</string> for 2 GB instead of 1024 MB. Finally, save the file and relaunch Sweet Home 3D. If Info.plist is protected, you may run a command like sudo nano /Applications/Sweet\ Home\ 3D.app/Contents/Info.plist in a Terminal window to edit it (this command requires to enter the password of the administrator of the Mac).
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/PropertyList.dtd">
<plist version="0.9">
<dict>
<key>CFBundleGetInfoString</key>
<string>Sweet Home 3D 6.0 Copyright 2007-2018 eTeks</string>
<key>CFBundleVersion</key>
<string>6000</string>
<key>CFBundleShortVersionString</key>
<string>6.0</string>
<key>CFBundleDevelopmentRegion</key>
<string>English</string>
<key>CFBundleExecutable</key>
<string>SweetHome3D</string>
<key>CFBundleIconFile</key>
<string>SweetHome3D.icns</string>
<key>CFBundleIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3D</string>
<key>CFBundleInfoDictionaryVersion</key>
<string>6.0</string>
<key>CFBundleName</key>
<string>Sweet Home 3D</string>
<key>CFBundlePackageType</key>
<string>APPL</string>
<key>CFBundleSignature</key>
<string>SH3D</string>
<key>CFBundleAllowMixedLocalizations</key>
<string>true</string>
<key>NSHighResolutionCapable</key>
<true/>
<key>LSMinimumSystemVersion</key>
<string>10.8.3</string>
<key>UTExportedTypeDeclarations</key>
<array>
<dict>
<key>UTTypeIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3D</string>
<key>UTTypeReferenceURL</key>
<string>
http://www.sweethome3d.com/</string> <key>UTTypeDescription</key>
<string>Sweet Home 3D Document</string>
<key>UTTypeIconFile</key>
<string>SweetHome3DDocument.icns</string>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeTagSpecification</key>
<dict>
<key>com.apple.ostype</key>
<string>SH3D</string>
<key>public.filename-extension</key>
<array>
<string>sh3d</string>
<string>sh3x</string>
</array>
</dict>
</dict>
<dict>
<key>UTTypeIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3DLanguageLibrary</string>
<key>UTTypeReferenceURL</key>
<string>
http://www.sweethome3d.com/</string> <key>UTTypeDescription</key>
<string>Sweet Home 3D Language Library</string>
<key>UTTypeIconFile</key>
<string>SweetHome3DLanguageLibrary.icns</string>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeTagSpecification</key>
<dict>
<key>com.apple.ostype</key>
<string>SH3L</string>
<key>public.filename-extension</key>
<array>
<string>sh3l</string>
</array>
</dict>
</dict>
<dict>
<key>UTTypeIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3DFurnitureLibrary</string>
<key>UTTypeReferenceURL</key>
<string>
http://www.sweethome3d.com/</string> <key>UTTypeDescription</key>
<string>Sweet Home 3D Furniture Library</string>
<key>UTTypeIconFile</key>
<string>SweetHome3DFurnitureLibrary.icns</string>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeTagSpecification</key>
<dict>
<key>com.apple.ostype</key>
<string>SH3F</string>
<key>public.filename-extension</key>
<array>
<string>sh3f</string>
</array>
</dict>
</dict>
<dict>
<key>UTTypeIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3DTexturesLibrary</string>
<key>UTTypeReferenceURL</key>
<string>
http://www.sweethome3d.com/</string> <key>UTTypeDescription</key>
<string>Sweet Home 3D Textures Library</string>
<key>UTTypeIconFile</key>
<string>SweetHome3DTexturesLibrary.icns</string>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeTagSpecification</key>
<dict>
<key>com.apple.ostype</key>
<string>SH3T</string>
<key>public.filename-extension</key>
<array>
<string>sh3t</string>
</array>
</dict>
</dict>
<dict>
<key>UTTypeIdentifier</key>
<string>com.eteks.sweethome3d.SweetHome3DPlugin</string>
<key>UTTypeReferenceURL</key>
<string>
http://www.sweethome3d.com/</string> <key>UTTypeDescription</key>
<string>Sweet Home 3D Plugin</string>
<key>UTTypeIconFile</key>
<string>SweetHome3DPlugin.icns</string>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
<string>public.content</string>
</array>
<key>UTTypeTagSpecification</key>
<dict>
<key>com.apple.ostype</key>
<string>SH3P</string>
<key>public.filename-extension</key>
<array>
<string>sh3p</string>
</array>
</dict>
</dict>
</array>
<key>CFBundleDocumentTypes</key>
<array>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>com.eteks.sweethome3d.SweetHome3D</string>
</array>
<key>CFBundleTypeIconFile</key>
<string>SweetHome3DDocument.icns</string>
<key>CFBundleTypeName</key>
<string>Sweet Home 3D Format</string>
<key>CFBundleTypeRole</key>
<string>Editor</string>
</dict>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>com.eteks.sweethome3d.SweetHome3DLanguageLibrary</string>
</array>
<key>CFBundleTypeIconFile</key>
<string>SweetHome3DLanguageLibrary.icns</string>
<key>CFBundleTypeName</key>
<string>Sweet Home 3D Language Library Format</string>
<key>CFBundleTypeRole</key>
<string>Viewer</string>
</dict>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>com.eteks.sweethome3d.SweetHome3DFurnitureLibrary</string>
</array>
<key>CFBundleTypeIconFile</key>
<string>SweetHome3DFurnitureLibrary.icns</string>
<key>CFBundleTypeName</key>
<string>Sweet Home 3D Furniture Library Format</string>
<key>CFBundleTypeRole</key>
<string>Viewer</string>
</dict>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>com.eteks.sweethome3d.SweetHome3DTexturesLibrary</string>
</array>
<key>CFBundleTypeIconFile</key>
<string>SweetHome3DTexturesLibrary.icns</string>
<key>CFBundleTypeName</key>
<string>Sweet Home 3D Textures Library Format</string>
<key>CFBundleTypeRole</key>
<string>Viewer</string>
</dict>
<dict>
<key>LSItemContentTypes</key>
<array>
<string>com.eteks.sweethome3d.SweetHome3DPlugin</string>
</array>
<key>CFBundleTypeIconFile</key>
<string>SweetHome3DPlugin.icns</string>
<key>CFBundleTypeName</key>
<string>Sweet Home 3D Plugin Format</string>
<key>CFBundleTypeRole</key>
<string>Viewer</string>
</dict>
</array>
</dict>
</plist>