can't mess up.. I never did it before and it worked perfectly. Make sure you back up your device first. Then follow the instructions as per the link below:
How-To Wipe with JL_Cmder - BlackBerry Forums at CrackBerry.com
It's actually quite easy but just requires patience. You won't affect your warranty at all. My torch was 2 months old and I was told by Bell that I needed to send the device for warranty...2-6 weeks and rent another berry ...to me that was unacceptable. So go ahead and make sure you have the latest desktop manager software and a copy of the latest OS.