Depends on what you mean by "format". Do you want to just wipe the data on it, restore the factory operating system setup, install a clan operatins system? All of your files you may want are backed up?
To wipe a system, download a disk wipe utility, download and burn the iso to a disk http://www.dban.org/download,
boot the laptop off it, follow the prompts and it will wipe the disk. To restore the OS, you should have either restore disks or a disk restore option on the hard-drive, check the manuals for your particular laptop.