thanks for your answer. Of course I’ve made a backup from my database with myAdminPHP and from the whole Website with ftp. Additionally I have exported everything with the Import/Export Add-On.
But to be honest I’m not shure if I have made some changes in the Templates and the Stylesheets? So this could be a Problem if I update the Theme. I could compare them to the original Files but I don’t have theme anymore. Any idea?