How do I access the ecm (pcm)? 1995 aurora

I have had a SES light come on intermittently. When it is on, there is a big clunk when you put the car in gear. It shifts smoothly while driving. After much research, It is either the speed sensor or the ecm. My question is if I get a used ecm to install (might as well start the cheap way) how do I access the ecm in the car. Thanks

1995 Aurora 172,000 miles. The ECM/PCM is located under the glove compartment - passenger side. You will have to take off the cover under there. The PCM slides straight up into the dash (kind of behind the glove compartment). There are 3 main plugs (color coded, I think) going into the PCM. Unplug those and retract the computer. There might be a release lever or latch.

I ended up buying a new computer after trying a used one first. To be safe, see if you can return the used PCM if it doesn't work.

One last thing. Unplug the battery before swapping PCM's.