Wirelessly posted (BlackBerry7520/4.0.0 UP.Browser/126.96.36.199 UP.Link/188.8.131.52)
Under Options then Security you press the thumbwheel and select Wipe Handheld. This erases everything from the database and delete aftermarket programs, as I recall. Then you can re sync.
I am now running 3.6 sp2 as I was advised by RIM to do. Hopefully, an update to 4.0 is forthcoming.