Regripping is very easy.
First, you're going to need to cut off the old grips with a blade. Then take off the tape.
Next, wrap some double faced grip tape around the top of the shaft, stopping about 1/2" above where the grip will be (i.e. you don't want to see the tape)
Next, while you're wearing rubber gloves, spread some naptha over the tape. Use a pan to catch the excess (something like a PIE pan or paint tray)
Put a little napta in the grip and roll it around to spread.
Then slide the grip on over the tape. Just try to make sure it's straight. You only have so much room and time to move the grip around on the club.
Then let it sit for about 24 hours.
For grips, I like golf pride tour velvet for irons and lamkin corded for woods.
You can get everything you need at http://www.dynacraftgolf.com/
As for sizes, there should be a chart on their site for hand / grip sizing. If not call their 800# and they can steer you through it.