From you cPanel go to your phpMyAdmin (this is the interface for your MySql database – where your wp content files live – & if your host doesn’t have you need a new host). In the sidebar, find your wordpress install – if you only have 1 site, it’s the only one there. Click on it. In the top menu click IMPORT. You will get a screen with a browse upload box – upload your backup. Click Go. Done. Good luck