Here is the procedure:
REMOVAL & INSTALLATION
See Figures 1, 2, 3, 4, 5 and 6
Fig. 1: The thermostat is located in the lower radiator hose on the 2.2L engine
Fig. 2: Remove the two retaining bolts for on the housing
Fig. 3: Separate the housing halves to access the thermostat
Fig. 4: Pull the thermostat out to remove it from the housing
Fig. 5: The thermostat has an O-ring which goes around the center
Fig. 6: Thoroughly clean the mating surfaces of the thermostat housing
When adding coolant, it is important that you use GM Goodwrench DEX-COOL® (orange colored, silicate free) coolant meeting GM specifications. On these vehicles, if silicated coolant is added to the system, premature engine, heater core or radiator corrosion may result. In addition, the engine coolant will require change sooner; at 30,000 miles or 24 months.
Disconnect the negative battery cable.
Properly drain and recover the coolant until the level is below the thermostat.
Unfasten the coolant outlet-to-inlet manifold attaching bolt and nut, then remove the outlet.
Remove the thermostat. Clean the inlet manifold and outlet mating surfaces.
Install a new O-ring onto the thermostat
Place the thermostat in the inlet manifold.
Attach the coolant outlet to the inlet manifold, using the bolt and nut. Tighten to 89 inch lbs. (10 Nm).
Refill the engine cooling system.
Connect the negative battery cable, then start the engine and check for coolant leaks.
2.3L and 2.4L Engines
See Figure 7
When adding coolant, it is important that you use GM Goodwrench DEX-COOL® (orange colored, silicate free) coolant meeting GM specifications. On these vehicles, if silicated coolant is added to the system, premature engine, heater core or radiator corrosion may result. In addition, the engine coolant will require change sooner; at 30,000 milee or 24 months.
Properly drain and recover the coolant to a level below the thermostat.
Unfasten the cover-to-outlet pipe bolt, which is accessible through the exhaust manifold runners.
Raise and safely support the vehicle.
Disconnect the radiator and heater hoses from the outlet pipe.
Unfasten the outlet pipe-to-oil pan bolt and the cover-to-outlet pipe bolts.
Remove the thermostat, then clean the old gasket material from the mating surfaces.
Fig. 7: Thermostat removal and installation-2.3L and 2.4L engines
Position the thermostat in ite correct location, then install the cover-to-outlet pipe bolt. Tighten the bolt to 10 ft. lbs. (14 Nm).
Install the outlet pipe-to-oil pan bolt. Tighten the pipe-to-oil pan bolt to 19 ft. lbs. (26 Nm) and the pipe-to-transaxle bolt to 40 ft. lbs. (54 Nm).
Connect the radiator and heater hoses to the outlet pipe.
Carefully lower the vehicle.
Install the cover-to-outlet pipe bolt through the exhaust manifold runner.
Properly fill the cooling system, then connect the negative battery cable.
I hope this is helpful. If you need more assistance, please let me know.