How did you take a backup? Using the data exporter plugin in the Oxwall Store or via host?
Via Exporter Plugin
Install Oxwall, install plugins and the data importer plugin then use the data importer plugin to upload your backup generated by the data exporter.
Via Host
If you did a full site backup via your host / control panel or something similar then this is a little different.
Id install Oxwall and all plugins you want to use then, if you created a custom theme then copy that over. Then take the sql of your database and insert into the new database.