On Macintosh...

Open the following folder: 

Finder/Go/Library/Application Support/SketchUp 2020 (or 2019...)/SketchUp/Plugins/

The Library is a hidden menu. To make it visible, hold down the "Option" key on your keyboard while you roll down the Go menu. Select the Library and it will automatically open the Finder window to continue. 

To uninstall your version of Render[in] on Mac OSX, simply delete:
  • AbventRenderin_3 folder
  • AbventRenderin3.rb

On Windows...

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