The installation procedure on Prestashop site is described here:
http://addons.prestashop.com/en/content/21-how-to
This documentation is old but fits perfectly to the current reality, all cases are precisely described and that’s why we decided not to re-write.
If the automatic installation process performed from the back-office is not working, follow also the instructions in this documentation, the manual installation procedure is fully described.
The procedure for updating is identical. The update via the back-office or via FTP does not overwrite your current parameters.