I found a laptop and its mark is gateway but i want to know how to reprogram it because i don´t know the password to it i want to know how i can reprogram it

If it is a newer laptop you should report it. The newer systems have a LOJAK style program in the bios that allows the owner to track its whereabouts regardless wether or not the system has been reprogramed. But as far as doing the programing goes you just need a retail version of windows (what ever distro you like) and change your boot settings in the bios to "boot from CD" or make cd rom your first boot device - it varies depending on the brand of bios and its version) then you stick your operating system in the cd rom drive and turn your system back on. when it asks to BOOT FROM CD: just hit enter and off you go. It will ask self explained questions during the install but Im sure you will be able to manage