To install the Render Boss Extension manually, just download the file via the button on the right.

Unzip its contents to their respective subfolders inside the ‘Scripts’ directory in the After Effects user folder. This folder is usually located at:

Windows:  C:\Users\{USER}\AppData\Roaming\Adobe\After Effects\{VERSION}\Scripts\

MacOS:  /Users/{USER}/Library/Preferences/Adobe/After Effects/{VERSION}/Scripts/

Restart After Effects, and the panel should be available inside the ‘Window’ menu.