ezjob - A theme is bunch of PHP files. So all you need is simply edit the PHP files. If you give us the URL and what exactly you want to change we might be able to help you more.

What theme(s) are you using? Different themes will give you different levels of control over what you can customize on them without having to know PHP and how to program. Most professional themes have a section in the backend of WordPress that allows you to make the customizations you're interested in.