Hi there hope i can be of assistance,
If you're going to change the thermostat you should gear up for a major job (straight forward, but long winded)1. Remove air filter box (for access).2. Remove drive belt, may well run round an engine mount, just secure out of the way unless it's worn.3. Remove outer timing belt cover.4. Set engine to TDC.5. Remove crankshaft pulley.6. Drain cooling system, remove timing belt, water pump and tensioner.7. Remove camshaft cover and then remove camshaft pulley.8. Remove rear timing belt cover.9. Remove two thermostat housing bolts (finally!)10. Flush cooling system and radiator with a hose11. Fit new thermostat with new seal.12. Refit rear timing cover.13. Refit camshaft pulley 14. Fit new water pump + seal and tensioner (if you've gone to all this trouble these components should be renewed).15. Fit new timing belt checking TDC and tensioner16. Refit outer timing belt cover.17. Refit crankshaft pulley using a new bolt to torque/angle setting as in Haynes.18. Refill cooling system with new coolant.19. Refit air filter, etc.
Also, while the belt is off, you can remove the water pump and inspect in detail. Basically check the fins for damage, and the bearing for any freeplay.
If you need further help, please ask