You can change the look of your stadium complex with many different themes! Your stadium will have a more personal look, and you can select better themes while you advance in your manager career. To change you theme, go to Stadium Complex in your account, and select the tab labelled "Themes".
If you can't see that tab, your career level is too low. Remember, the required career level to access the first themes tab is 40.
Some of the themes have no general purpose besides their look, some of them will also increase your reputation, with the points shown in the Theme description.
You can see all the Themes and description in the Themes Tab, but you won't be able to use it until you have the career level required for that theme.