[Britwrench]

Is the engine overheating, do the cooling fans work correctly, does the heater work as it should and provide constant hot air when operated? Temp gauges on these cars are not an accurate guide to the actual readings.
So before you do anything make sure you really have a problem and not a mis-reading gauge.

To bleed the cooling system, turn the heater on to the full hot position, make sure the coolant level is to the very top of the tank and start the engine, carefully loosen the 12mm headed bolt that is on the top hose outlet at the front of the cylinder head and wait until coolant flows out of it, continue to top up the level and wait until the thermostat opens and the cooling fans cycle, once the above has been done check coolant level when the engine is cold.