If you go to ThemeForest, download the Restaurant theme again – that will be the latest version 5.5 – and then upload this to replace the existing copy you should find everything goes back to normal.
Bear in mind, that if you’ve made any custom css changes, then you’ll need to copy them over to the new style.css once installed to make sure everything stays the same.
Updating via FTP instructions are below if you’ve not done this before.
Double click on the zip file you’ve saved to your desktop to extract the theme files. Inside the unzipped folder you’ll find a number of files, including documentation, import files and the theme folder.
Using your chosen FTP client or via your hosts Cpanel, upload the theme folder via ftp into the themes folder on your hosting account to overwrite the existing/older version of the theme.
Please note: We always advise fully backing up your site and keeping a copy of any customisations you’ve made prior to making any changes on your site.