Thank you both, I'll have a look at this during the week and post back what I find after making the four changes. Thank you for clearing it up for me, as you can tell, this isn't my bread and butter, but much appreciate the help.
My parents had this changed a while ago, but didn't mention any problems etc. reported by the installer - Hopefully it was just lack of knowledge, rather than an outstanding problem. Fingers crossed!
Thank you!