Frost & ice were building up inside the top of our upright freezer, so I replaced the door gasket. First I'll make my long story short, then I'll tell the longer story for those who might be interested and might benefit from my experience.
Short version - The whole project took about three hours, but less than an hour of that would have been required if I were more of a handyman and if the freezer hadn't had prior work done on the door for the same frost buildup problem.
Long version - When our freezer first began experiencing frost buildup several months before, I called out a handyman to fix it. Apparently this freezer model is prone to ice building up inside the molded plastic shelves in the door panel. That had happened to our freezer and had caused the door to sag and get out of alignment. The repairman removed the door so he could remove that built-up ice. This included removing the door panel and door gasket, then replacing them, and remounting and realigning the door. When he reinstalled the old gasket, he used silicone to attach it to the door. Removing that old silicone is what took most of my repair time.
Had I not had to deal with the old silicone, the job would have simply consisted of loosening all the screws holding on the door panel (screws hidden under the gasket), pulling out the old gasket, installing the new gasket, and retightening the screws.
I'm not a great handyman, but I believe just about anyone can do this job. Remember, though, that simply loosening the screws and pulling out the old gasket does not necessarily mean that the door panel has loosened enough so that you can easily slide in the new gasket; the panel can get hung up on the screw threads and leave too narrow a gap. Gently pry the edges of the panel out a bit to increase the gap. Also make sure you're sliding the right part of the new gasket into the channel behind the door panel; I first tried inserting the wrong part of the gasket and thought the gasket was a good inch too small for my door, but it was just my mistake.
I also suggest checking for instruction videos before tackling the project, if you're unsure of yourself. One such video suggests only removing the top half of the old gasket before starting to install the new one; I think that was a good idea because the lower half of the old gasket helped hold the door panel steady as I installed the top half of the new gasket.
I used a hair dryer on low heat to try and straighten out kinks and ripples in the new gasket prior to installation. The gasket had been packed very carefully, though, and there really weren't many true kinks, and those weren't particularly bad. I eventually gave up being able to get rid of the small ripples in the gasket (and there were quite a few), so I just went ahead and installed the gasket, and it worked fine.
The difference this project made was immediate and amazing. The new gasket produced a seal like the door had had when the freezer was new. A week later I'm still having to get used to having to give the freezer door a good tug to get it to open now. The freezer still had just a bit of frost and ice which I had not been able to fully remove before doing the repair, but every bit of ice and frost disappeared within a few days of replacing the gasket.
I'm very happy with the results, and I urge anyone having similar problems not to wait months before tackling the project like I did. It's really quite simple if the old gasket has not been stuck in with silicone adhesive as mine had been from the previous repair work.