The safest way to do so would be using a site called WotanServer. It is a payed service, but it the easiest way to go without getting into a mess. It is possible for free, but it is a manual process and believe me it's not easy (it took me 6 months just to find the files for my K800i lurking on the net, yet alone learning how to apply them!). All you will need for this process is a DCU-60 cable, which should have been supplied with your phone. If you have any questions, I'll be happy to answer them, although most of the information is avaiable on the WotanServer site. Good luck
To debrand means to get rid of any operator icons, features or restrictions on a handset. it can often result in the handset performing faster and the menus looking a lot nicer as well.