Apply new branding to existing Wordpress theme

We've bought a wordpress theme and are very happy with functionality. A new image branding has been completed and should be applied to the theme to make everything uniform; in other words, it's mostly fixing the colours and ensuring the group branding is uniformly applied to the site (defaults are set) and that it is pleasing to read. Also required, is a transparent version of the logo PSD of logo is available for colour scheme and transparency.