Implement design into php script

I recently purchased a script written in php code. The script comes with a header, footer and css files so that customisation is easy. I have made the design I would like implemented. The idea of this is project is to implement this design into the script and keep the style constant through out. There might also be code modification required to edit the functionality of the homepage and some other features to make it display the way I want it to. The project is pretty much basic and shouldn’t take long.