I'm halfway through changing my Matrix as we speak. Its tricky but not megger difficult and believe me I'm no mechanic

My heater was also sh!te so I decided to remove the bypass and copper tube it, big mistake! Two days later, a drip at my feet, fogging screen and the lovely smell of red hot coolant

If you do decide to change it, print off RJs guide (cheers RJ) and use it alongside the Haynes.