The first step is to download the extension. Once you have downloaded it, unzip the files to your local computer.
Using an FTP program such as Filezilla, CuteFTP, etc. you will now upload PHP files into “includes/ext/” folder on your server. If extension comes with template files, you will need to upload them to “templates/your_template” folder.
All files should be uploaded in ASCII format (also known as “text” format).
Some extensions may require you to install them first. To do that, login to the control panel and browse to “utilities - extensions” where you can click on the “install” icon next to your extension.