Instalation
1) Close 3ds Max.
2) Copy the file "RadialSymmetry.dlm" from the folder that matches your 3ds Max version to your "plugins" folder in your 3ds Max instalation directory(C:\Program Files\Autodesk\3ds Max xxxx\plugins)
3) Open 3ds Max and look in the modifier list for the modifer "Radial Symmetry".


Updatig
Do the same steps like the on the Instalation but replace the existing "RadialSymmetry.dlm" file


Uninstallation
Delete "RadialSymmetry.dlm" file from the plugins folder in the 3ds Max install directory.