Depends on how long ago you changed it. A thermostat is not something to upgrade, just replace it when it doesn't work. Some people on the forum suggest a 180*F theremostat, but I believe in sticking to the stock 195*. If you don't know when it was last changed, and if you are taking the housing off anyways, no harm in changing the thermostat.
The symptoms of a failed thermostat is your car will not heat up to normal operating temperatures during the winter. The thermostat stick open and coolant flows to the rad no matter what temp the engine is at.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)