The following instructions are for Joomla! series 1.0.xx, but series 1.5 is very similar, the main difference being that the installers have been combined.

• Download the template to your computer and save it in a handy place (desktop?)
• Do not unzip it.
  
• Go to your administrator menu installers>template-site and find the upload path and click "install"
• On completion you'll be taken to the template chooser menu. Click the radio box for your desired template and choose "default" higher up the page.

Alternatively, if you have a lot of templates and you want to install them all and have a close look at them, you can do the same job as the installer if you just unzip them and put each template folder in your "templates" directory on your Joomla! site, as follows:

• Download the templates to your computer that you want to check out a little closer, installed on your site.
• Unzip them all into a folder. (Keep them in their unzipped folder structure)
  
• Using FTP log into your account and transfer all the template folders to your site template folder.
• OR
  
• If you are using your cPanel control panel, choose "file manager", change to your templates directory and choose upload. Find each template folder upload path and upload them.
• Go to your administrator panel for Joomla! and choose the menu site>template manager>site-templates and cycle through the templates making each the default and using another browser window, look at the front end of your site, refreshing after each change
• Eventually after you've made your final choice, best to remove the other templates so you keep your site tidy and lean !
• The above viewings are easier to do if you have installed a web server on your home computer. Go here to find out how to do that. (Section entitled: Running and Testing Joomla Without a Hosting Account)