Create a themes directory in sites/all.

sites/all/themes

Themes placed in the sites/all/themes directory will be available to all sites sharing the same code base. If you are not using multi-site then just put everything here for now.

The basic instructions are as follows: Download the theme, extract the files, upload the resulting folder, and enable and configure the theme in administer > site building > themes.

The detailed instructions are:

1. Download the theme：Buy a theme ,Login topdrupal.com,click "your name",click "Files",click Filename start download.
2. 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
3. Upload the folder. FTP/Copy/SCP your files to the desired themes folder in your Drupal installation. Since the /themes/ folder is typically reserved for Drupal core themes, you should create a sites/all/themes/ directory and put uploaded themes there. This will also make it easier to update your Drupal site later on as your themes will not be mixed in with core themes.
4. Go to http://jquery.com , download jQuery 1.3.x(jquery-1.3.2.min.js),Rename the file(jquery.js) and use it to replace misc/jquery.js.
5. Enable the theme. Go to administer > site building > themes. Check the 'Enabled' box next to the theme and then click the 'Save Configuration' button at the bottom.