It looks like you have an ARM (Adjustable Rate Mortgage). Depending on how much time you have left on your loan and what index your ARM is pegged to, it may or may not make sense. Its best to talk to a Mortgage Lender for this one.
Conventional loans can be either adjustable of fixed. adjustable rates can change, fixed cannot.
You can contact the loan officer you used and simply ask them if your rate is adjustable or not or you could check your paperwork from closing. The HUD1 will indicate this on page 3 or 4 where the terms of your loan are clearly indicated.
You may have an adjustable, or you may have paid a little upfront to buy the rate down to the 2.76% rate you've indicated and it's a fixed rate, without seeing your closing paperwork no one here on Trulia can say for certain.