Its easy mate, nothing to worry about.
Do it when the car is cold for minimal coolant loss.
Take the engine cover off and look down to the right of the engine between the block and the airbox. You'll see the coolant hose running towards the back of the engine.
The sensor is on there, you'll see the plug on the sensor so just unplug that (test fit the new ones you have to decide which one fits)
The sensor itself is held in with a plastic clip, prise that off with a screw driver (have the new sensor ready)
Pull the old one out and put the new one in, make sure the rubber O ring is on it.
Insert plastic clip back in and plug the wire back onto it.
Top up coolant as required and jobs a good one.
Takes less than 10 minutes