My garage door opener is no longer functioning. Anyone know how I go about replacing it? I am assuming it cannot be repaired.

Go to a store that sells them, buy a new one, arrange installation with them or someone on craigslist, celebrate by opening and closing newly functional door once for every year of your life.

Thanks, Smittyhoo. I actually do not need the whole apparatus replaced. Just the little hand-held remote device that opens the door from far, far away. But maybe the stores that sell the whole apparatus will have a way to replace the little hand-held remote device. I have emailed Liftmaster and am waiting for their response.

Mine went out last week. All you need to do is replace the battery inside the opener. I took my opener to Batteries Plus near Anderson and Burnet and they opened it up and replaced the battery for me for less than $5.
-Amanda

Thanks, Amanda!