There are many things that can cause buzzing and we can't always be sure where it's coming from.
1. Check truss rod nut if there is one. Slightly tighten it. (or ask repairman)
2. Make sure your strings are installed correctly.
After you loosen the string with enough slack, push the ball end of the string into the bridge wire hole while gently jiggling the bridge pin with your fingers. You'll feel the ball end go into the guitar body, removing pressure against the bridge pin. The pin should now pull out very easily with your fingers, however if it is still stuck tighter than your fingertips can handle, I bought a very common plastic string winding tool at a local music store that has one end shaped like a U. Put the head of the pin in the U and gently rock it back and the pin comes out.
NOTE: The other part of the plastic tool is a crank so you can turn the tuning pegs fast. I don't recommend that part. Buttons can unscrew and come off before you know it.