Installing themes to Joomla 1.5 is just as easy. Here are very basic instructions (very similar to the original Joomla version).
1. Log into your FTP
2. Open the folder “templates”
3. Upload the unzipped theme folder
4. Log into your Joomla 1.5 administration
5. On the top navigation bar, click “Extentions” > “Template Manager”
6. Click on the theme that you would like to chose
7. Click Default on the upper right corner and that’s it!
