Check out this Replacing a Bathroom Faucet Step-by-step at This Old
House Online:

http://www.thisoldhouse.com/toh/how-...615503,00.html

Even if you bring on a contractor, it's still good to know from a
reputable source what is expected to be done in a repair like this.
You can also take a look at the tools ans shopping lists to see what
your contractor should be using.

Hope this helps,
Tabitha