On Macintosh...

To uninstall your version of Render[in] on Mac OSX, simply delete these two items:
  • Abvent_Renderin3 folder
  • Abvent_Renderin3.rb

You will find them at the following path:
"Macintosh HD/Users/"your name"/Library/Application Support/SketchUp x/SketchUp/Plugins/

On MacOS 10.7 or higher,  the Library folder is hidden. To reach it, go to the Finder menu and click "Go" while you hold down the Option key on your keyboard. This will make appear the Library in the roll down menu. Select it to open the appropriate Finder window.  

On Windows...

Use the standard Windows Tool to uninstall your version of Render[in]