If you installed them from Flash Builder you just need to go to the common extensions folder and delete folder that matches your extension ID.
All extension are copied to a common location, the extensions folder in the CS Service Manager (CS5ServiceManager or CS5.5ServiceManager). This is found at:
In Windows XP:
C:\Documents and Settings\<user>\Application Data\Adobe\
In Windows Vista:
In Mac OS:
If you installed them via Extension Manager you can delete them from Extension Manager by selecting the extension and clicking Remove.
Hope this helps.
Thanks worked perfectly.
Worked for me driving me crazy for awhile.