How do you replace thermostat? I tried to do it and it wouldn't fit

Step 1 Park the Sunfire on a flat surface. Open the hood and allow the car to sit until the engine is cool to the touch. Unscrew the cap from the coolant overflow tank. Lift the front of the car with a floor jack and set jack stands under its subframe rails. Lower the vehicle onto the jack stands. Step 2 Remove the bolts securing the splash shield directly under the radiator, using a ratchet and socket. Lower the splash shield. Position a drain pan directly under the radiator drain on the passenger side of the radiator. Turn the radiator petcock – the plastic thumbscrew – counterclockwise to open it and start the flow of coolant from the engine. One the flow of coolant stops, close the petcock. Reinstall the splash shield and tighten the bolts until they are snug. Lower the vehicle to the ground. Step 3 Trace the LOWER radiator hose toward the engine until you find the thermostat housing – the metal housing that connects the lower hose to the engine. Remove the two bolts that secure the lower radiator hose coupler to the thermostat housing and pull the coupler away from the housing, exposing the thermostat. Pull the thermostat and gasket out of the coupler or housing – it can remain in either. Step 4 Clean the mating surfaces of the thermostat housing and radiator hose coupler with a wire brush and clean, lint-free cloth. Install a new O-ring – included with the new thermostat -- around the circumference of the new thermostat. Guide the thermostat into the housing with the spring side pointing into the housing. Position the coupler back in place on the housing and tighten its bolts to 89 inch-pounds, using an inch-pound torque wrench and socket. Step 5 Fill three clean, sealable 1-gallon containers halfway with new Coolant and fill them the rest of the way with cool, clean water. Seal the containers and lightly shake them to mix the water and coolant. This gives you 3 gallons of 50-50 mixed coolant and the Sunfire's 2.2-liter engine holds roughly 2.5 gallons. Step 6 Fill the overflow tank with the mixed coolant until the level holds steady at the “Max” mark. Open the bleeder valve – the small metal nipple – on the top of the thermostat housing by turning it a full turn counterclockwise with a six-point, box-end wrench. Continue adding coolant to the overflow tank until fluid bubbles from the bleeder valve, then close the bleeder valve. Step 7 Start the engine and allow it to idle until the upper radiator hose feels hot, and check for leaks. As the engine idles, the coolant level will drop. Add Correct Coolant to bring the level back up to the “Max” line. Repeat the topping off of the coolant until the level remains consistent at the “Max” line. Step 8 Take any old coolant to a used automotive fluid recycler or a local auto parts store for disposal.