A factory reset will destroy EVERYTHING on the hard disk so back up all your important files, browser favorites, email settings, and anything else you want to keep.
Then go to the fujitsu siemens web site and look for the support page for laptops.
This will tell you how to do a factory reset.
Or look in the documentation that came with the laptop.
It normally consists of doing nothing more than pressing a button or two during computer start up, though exactly WHAT button to press does vary from laptop to laptop.