hey guys im new to the forum and have searched through the threads but didnt find what i was looking for..

I recently purchased a 2010 MacBook (Not PRO) from a guy, not gonna mention from where (CraigsList) and everything is fine but i cant download apps or install new software because im asked for an Admin PW. As you may suggest when i texted him about it i got no response.

So the million $ question here is "How do I change my Admin PW without knowing the current one?"

Any and all advice gladly taken.