WordPress really is a great product. In essence it has the ability to provide a fully functional website in minutes with its unique and very simple to use 5 minute installation. With that said a lot of users of the WordPress content management system will at some point feel the need for a new and interesting design.
These people will often think that makes a new design and having it work the way they want is as simple as editing a few images in a program such as Photoshop. These people are far from correct.
You could edit the images as previously mentioned; however this will give you a basic design just with some small minor changing. In other words this will not make your website look very different and it is just be exactly the same functionality wise. However if you were to hire a WordPress developer along with a website designer, you could have the two draw up a design which has a fully coded backend system to make sure it runs as you desire, making the WordPress developer just as important as the website design in any given scenario.