In case you wish to perform a clean Modelur installation, but already have an existing one, please do the following:

1. Close SketchUp
2. Download latest Modelur installer file (remember where you saved it, you will need it in step 5)
3. Windows: open %appdata%SketchUp\SketchUp SU_VERSION\SketchUp\Plugins\
   OS X: open ~/Library/Application Support/SketchUp SU_VERSION/SketchUp/Plugins/
4. Delete modelur.rb file and /Modelur folder in folder from step 1
5. Right-click and extract contents of RBZ file (which is just renamed ZIP file) to this same location (you shall see back modelur.rb and /Modelur)
6. Start SketchUp