A tuning peg broke on my acoustic guitar. What do I need to do to replace it?

I have an alvarez rd20sc blk. My guitar was leaning up against the couch when it fell over, and broke the peg to the fourth string. I'm planning on buying some new tuning machines for the guitar. Are they all the same as far as installation goes? If so, how do I find the right ones for my guitar? Would it be easier to install them myself, or let someone else do it for me?