- Download the theme.
You can find themes on http://drupal.org/project/themes, as well as some external sites. Make sure the version of the theme matches your version of Drupal. Note that themes labeled "DEV" are in a development stage. They may be written for a previous/current/future version of Drupal, and they are considered unstable and should be handled with care.
- Extract the files.
When you first get the theme, it will appear in a compressed file format such as 'tar.gz'. On Windows, use a program like 7-Zip to extract it. On the Mac, you can use Stuffit Expander. To extract the file using the Unix command line:
tar -zxvf themename-drupalversionnumber.tar.gz
You should see a list of files extracted into a folder.
- Upload the folder.
FTP/Copy/SCP your files to the desired themes folder in your Drupal installation. Since the themes folder at the top level of Drupal is typically reserved for Drupal core themes, you should create a sites/all/themes/ directory for contributed(non-core) themes and put uploaded themes there. If you are running a multi-site installation of Drupal, you can create a themes folder under sites/my.site.folder and put themes there that are specific to a particular site in your installation. Themes that will be shared between all sites should be placed in sites/all/themes.
- Read the directions.
If the theme has an installation file (usually INSTALL.txt and/or README.txt), read it for specific instructions. There are themes that require special treatment to function properly.
- Enable the theme.
Go to administer > site building > themes. Check the 'Enabled' box next to the theme.
- Optional: Make it the active, default theme.
Check the 'default' box to make this the chosen theme for your site. Enabled alone will allow users to select the theme, if you have allowed that permission.
- Click the 'Save Configuration' button at the bottom.
If you run into problems, check the themes issue queue and search the forums. If your problem hasn't already been addressed, post a question and someone will try to help you out.