Knowledgebase
How to enable, disable and edit the settings of themes in Drupal
To enable and disable installed Drupal themes and to change their settings, log in to the admin panel of your Drupal and click on the Appearance tab in the toolbar. On the page that opens (the List page) you'll see all the enabled and disabled themes. Next to the screenshot of each theme there are some buttons. To enable a disabled theme or vice versa just click on the Enable or the Disable button. An enabled theme that's not the default one can also be set to be the default one by clicking on the respective button. The default theme is the theme that is displayed to all visitors on your site.
At the top right corner of the page there are some sub-tabs: List, Update, Settings. You can use the Update sub-tab to check for updates for the themes that you've installed. Click on the Settings sub-tab to change the settings of any of the installed and enabled themes. After you click on the Settings tab you'll see some small buttons just under the tab. There should be a button for each of the enabled themes. To edit the settings of a theme simply click on its button. Many of the settings are the same for all themes. The Toggle Display section let's you hide/show the logo, the site name, the main menu, etc. From the Logo Image Settings and Shortcut Icon Settings you can change the default logo and favicon that come with the theme. To do this, unmark the checkbox for Use the default logo/Use the default shortcut icon, then use the Browse button that appears to locate the new image on your local computer, and click on the Save configuration button to upload it.
Some themes have extra settings that can be configured. For example, the Bartik theme that comes prepackaged with Drupal has settings which allow you to change its color scheme.
For screenshots and some more details you can also check out the tutorial on how to manage themes in Drupal.