I'm just wondering if anyone here changed out their thermostat by themselves. When I was considering to change it myself, it looks kind of hard because of the tight space to access the thermostat.

its not hard. just drain some coolant from the radiator (or don't), unclamp the two hoses going into the t-stat, pull them off (put a towel underneath to catch the coolant that will leak out), remove the 3 bolts, swap the t-stat & gasket, then put everything back together. if you're still running the OEM intake, you'll probably have to pop loose the air duct too.