How do I remove the crossover exhaust pipe from pontiac Montana 2000. Im trying to change the thermostat

You don't need to take that pipe off. It's not a fun job but it can be replaced with the pipe on. More of a pain to take it off anyway. A 13mm ratchet wrench will get the lower bolt loose. I replace these all the time at work.. Some you need to take the throttle body off some not. About a 1 hour job with bleeding out cooling system, but I've done a lot of these. Patience and it will come off.