1) From the main page, go to Personal > My Site.

2) Choose the "Control Panel" link in the top right corner.

3) Choose "Theme Settings" from the left control panel menu.

4) Click the "Customize This" link next to the theme listed next to your theme name.

5) Make the changes you want, and preview the theme by clicking the "Preview" button at the bottom right of the "Customize This Theme" window.

6) If you like what you see, click the "Apply Changes" button.

7) If you like, you can name your custom theme, and publish it in the Groupee theme directory.