I Need Redesign An Existing Website Which Contains PHP, SQL & Html. HOW?

Hello, I would like to redesign an existing website in dreamweaver which contains php, sql & Html. The new designs have already been made on paper and usability issues have been sorted out. I just need to make the old site look like the new designs while still insuring all of the existing code in the old site still works. I make a free templates and then just copy small pieces of code in at a time or alter the existing pages which contain the code.

Thank you