Do I need to uninstall RTMM add-on before installing new version. What is best way to uninstall?
New version of what? Sim? From what to what? Like from P3Dv4x to P3Dv5x?
If so, to remove the RTMM Add-on (P3Dv4) delete it's main folder from the default add-ons P3Dv4 folder
To add the RTMM Add-on (P3Dv5), download it, extract the zip and place the main RTMM Add-on (P3Dv4) folder into the default P3Dv5 add-ons folder.
Start your sim and enable the RTMM Add-on (P3Dv5).
DONE.