The skin, (how the game looks), can be changed by doing the following:

Click on Account in game.
Select Display.

Here you can change the Display Width, and also select a Game Skin. There are several available. Select which skin you prefer to use, and then click on Update next to your selection, you should see the changes immediately.

The Display width can be changed by doing the following:

In the middle of the Display options page, you will see the word Display, with "Display Width:" and a number. you can change this number to anything between 650 (the game will appear smaller, the borders pulled in), to 1050 (the game appears wider).