Need to Bypass Starting Password Prompt in Mac Desktop

I recently bought a PowerBook G4 which not completely brand new. I bought it from my cousin’s friend. The problem is I don’t want to enter any password every time I start the machine. Every time I start the machine it prompts a window to enter password. It is a bit annoying to me. I have searched for the option to disable it but remain unsuccessful. I am not really sure whether it is removable or not. Could it be removed? If you have the answer please send it to me as soon as possible.
