Maybe the following link would be worth a look:
Uninstalling previous versions of Silverlight from Windows
http://www.microsoft.com/getsilverlight/get-started/install/uninstall-win.aspx
If you cannot uninstall from Add-Remove Programs...the following freeware may be useful:
(FWIW...it's always a good idea to create a System
Restore point before installing software or updates)
***Proceed At Your Own Risk***
Revo Uninstaller - Free and Full Download
http://www.revouninstaller.com/revo_uninstaller_free_download.html
(Windows XP, Vista, 7 - 32 bit operating systems only)
(The full retail version supports 64 bit operating systems)
How to uninstall programs with Revo Uninstaller
http://www.revouninstaller.com/revo_uninstaller_how_to_uninstall_program.html