Hello soundmodel and welcome to these forums. You'll find many helpful people here and a lot of useful information. Make sure that you:
Put them in
C:\Users\me\AppData\Roaming\REAPER\Themes
or even easier: just drag the .ReaperThemeZip file into REAPER's arrange view.
"InstallData" is used only during installation, as far as I know. Why it is not tidied up at the end of the installation process is a mystery to me.