You NEED to refinance if you're at 4.75% brotha!!! There's a lot that goes into your rate (credit score, loan-to-value, etc., etc., etc.) but you're definitely high for what the market rates are currently.
In layman's terms, if you keep paying your same monthly payment you are right now, a lesser amount will be going to interest (you simply giving the bank $ for the privilege of them lending you $) and more will go to your principal (the actual amount you owe on your home until you own it outright). If you kept your same payment, you'll likely pay it off in less than 5 years (ballpark...without me doing all the math).
@Ron has some good contacts he can probably turn you on to.