Before you replace the opener, make sure your door is still working properly.

You should have some kind of manual disconnect of the opener from the door (sometimes a red rope dangling). Once you’ve confirmed you’ve disengaged the opener, with your hands try to lift the door up. It should be pretty easy. This should not be a struggle at all. Now try to pull it down. That too should also be easy and little muscle effort. You shouldn’t need to exert much force either way because the springs on your door do most of the work.

If it is hard to lift either way, you have a door (or more likely spring) issue. Replacing your opener won’t fix your problem. Get garage door service. Also, if you aren’t REALLY REALLY experienced with garage door springs, don’t mess with them. There is a tremendous amount of force stored in them, and if you do it wrong, all that energy will come out and once and could maim or kill you. Garage door service doesn’t have to be crazy expensive. A couple hundred dollars is what it cost to have my springs replaced (parts included) a year or two ago.

Don’t take chances with your life.