How To Install A Drupal Theme
If you are not so impressed with the default themes that come with Drupal cms, you can go to Drupal Themes and select the Drupal theme that does impress you.
Select Drupal Theme
There are several hundred different themes available so you can limit the number of displayed themes by using the "filter by compatibility" block located on the themes page.
This way you can search for themes compatible with your version, either 5, 6 or version 7. Take your time and read the descriptions that come with each theme. Read the Features information, this will give you a synopsis of the themes most important characteristics. When you have selected your Drupal theme, download it.
Download Drupal Theme
The next thing you have to do is download your Drupal theme to your PC or Mac. Untar or Unzip it with 7Zip or Stuffit Expander. Read the read me file. I use PSPad at this point to read the files and check for any additional installation instructions.
Check for any dependancies, these are files that your theme needs to function properly. If there are no dependancies its time to upload your Drupal theme to your server.
Upload Drupal Theme To Your Server
If you haven't done so already, create a sites/all/themes/ directory on your server.Use FTP to upload your Drupal theme to the themes directory you just created.
If you use a LAMP or a WAMP stack on your computer like Bitnami stack you can copy and paste it to your themes directory.
Enable Your Drupal Theme
The image below is of an average themes directory. You may have a few more themes in the directory. It's good to keep a default theme like Garland for updates.
Enable the theme by selecting it. Select it as default as well. Each theme has its own set of configuration options. When you save your changes that's it, have fun with your new theme. Any questions? Leave a comment.
For more information check out the theming guide at Drupal.org.