My wifi changed to my friends after my friend used it?

okay so my friend connected to my wifi on his laptop at my house ( i dont have a password for it) ao then after i trired to connect to it on my ipod touch my wifi had changed to his router name from his house plus its password protected. if it means anything when he connected it asked for a code from the router so he put the number of the router into his computer. please help me get my router to appear as what it did before my dumb friend got on it