HI, i have a problem

in some server i get kicked after some time, and the servers says: "bla bla bla update your client m2 bla bla" and i get kicked after that

ik someguys will say "go to fb of iw4play and download new version" but i dont know what i have to download and how to update the client!!
cause i downloadded from the pirate bay!!

can you guys explain to me and give me the link here?? =S