hey i got a 1996 jeep grand cherk my heat is all over the place... some times its hot sometimes its cold .. hot than slowly turns cold my buddie tells me it might be my thermostat what do you guys think? and if it is where would i find it.. ? thank youu

Check your coolant level in the radiator and the overflow bottle. Make sure you check it with the engine COLD.

ok but how do i replace it?

This (http://www.autozone.com/az/cds/en_us/0900823d/80/15/20/b1/0900823d801520b1/repairInfoPages.htm) describes the procedure for the 4.0 I6. I'd still check your coolant level first, dksob81 has the right idea where to start.