Its a really easy swap. If you open the hood, look down on the driver's side of the firewall. You'll see a big wiring harness that plugs into the PCM which is sticking through the firewall. The harness bolts to the PCM with a 10mm bolt in the center. There are two other bolts on each side of the PCM, remove those.

Once that is done, in the cab by the parking brake you should be able to pull the PCM out. There's a calibration code that needs to match up to the new PCM, it's on a decal on the PCM. Take it with you to the dealership, or some auto parts store can get you a refurbed PCM for a lot less.

 

I used to program performance chips and have pulled out many PCMs from different Fords. One thing I am not 100% sure on because it's been years since I removed one from that year truck is if the parking brake assembly makes it tough to pull out the PCM, so you might have to loosen the bolt on that if the PCM doesn't jiggle out.

It's tight space under there, so if you're a big guy, if you have a significant other who's smaller and can pull it out once you've loosened it, that'll help.

I show that rockauto.com carries them and lists the calibration codes they have available. Go to Ford -> 1996 -> F250 -> Electrical -> Engine Control Module.

I'm not saying to buy from there, especially if you're not sure the computer is the problem, because it's harder to return something via mail! But it's a good reference to see what calibration codes look like since there are several numbers on the PCM, and not all of them are calibration codes.