1. Download a new theme package from www.zerotemplates.com.

2. Read any README or INSTALL files in the package to find out if there are any special steps needed for this theme.

3. Upload the contents of the theme package to a new directory in the themes directory in your Drupal site.
For example;
◦in 4.7 you place your theme in themes/checkers_red.
◦in 5.0 you place your themes in /sites/all/themes/checkers_red

4. Click administer » themes and enable the new theme (Drupal will auto-detect its presence).

6. Next edit your user options and select the new theme. If you want it to be the default theme for all users, check the default box in the themes administration page.

For more help visit http://drupal.org/