First of all, I have to apologise for being such a novice!
So I have copied across the .php files that I'd like to edit my from parent theme (twentytwelve) to my child theme and edited them there.
These changes have taken effect no problem on my localhost site but when I made the website live the .php files have not been overridden. The changes I have made to the style.css files have worked perfectly.
Am i missing something?
Any help would be much appreciated!