Unfortunately, there are no forms on the web for a motion to terminate probation early in New Mexico. Your best bet would be to ask for a blank form from the clerk of the court where his case is being held.
The key to this motion is not so much the form, in my experience, but whether probation agrees to let the probationer go. I've seen probation terminated favorably upon an oral application (no written motion) if the probtioner and his PO both agree that further probation is unnecessary
Here's a file showing what probation wants to see before recommending early probation in your state. As you can see probation and a judge will generally entertain a request for early termination of probation when you have finished at least half of your sentence, if a probationer has not been in any trouble while on probation, if he owes no fines or fees and if he has completed all of his special conditions. So these are the facts above that you want to include in his motion.
If his probation officer is going to back the defendant up before the judge, he should make it clear in the motion that his PO thinks he is ready now for the termination of your probation. If probation approves of the motion, in my experience the odds of the judge granting the motion is very high. If probation opposes it, the judge will likely rule with probation.
So in short, a successful motion begins first with conferencing the early termination with the probationer's PO and getting his approval.