Hello m8, this is a piss easy job. First get a hard drive from www.ebuyer.com. Then backup all your saved game data onto a usb flash drive or external drive. Then disconnect all cables and swith the ps3 off at the back. Open the flap which covers the hard drive, take a philips screwdriver to the hard drive caddy, push it to the right and it pops out. Take the drive out the caddy, put the new one in, screw it back into place, put the flap on, put all cables in and power on, follow on screen instructions to install the playstation OS, do a system update, copy saved game data back onto hard drive.

Job done in half an hour I'd say.