If an add-on is obtained from a source other than the X-Cart App Store, you can upload and install it as follows:
In your store’s Admin area, click My Add-ons to open the My Apps page of the X-Cart App Store:
On the My Apps page, locate the Upload add-on button and click on it.
A pop-up titled Upload add-on appears.
In the Upload add-on pop-up, submit an add-on package by clicking the Select file button. The file should be a .tgz, .tar.gz, or .tar archive. The installation process starts. Once complete, the add-on falls into the list of installed add-ons.