On the first page of the Restore section, you will be asked to enter the root password of the system, and to confirm the disclaimer. The disclaimer indicates that the restore procedure will completely erase your existing data, and replace it with what is in the backup file. In the event the restore fails for some reason, you may be left without functioning In-portal data. 
Once you click next, you will be taken to the installation screen. It is not possible to be in the administrative console at the same time the restore is taking place, as all of the existing data, including the sessions and the user information, is erased.