Download a fresh copy of the Theme from Themeforest. 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 themes zip file. Double click on the second zip file to extract it and get the theme folder. Move this onto your desktop.
Log into your hosting accounts Cpanel, and access their FTP service. Go into your hosting accounts files and folders and locate the WordPress folder, inside there click on WP-content folder, inside of there you’ll see the themes folder. Go into the themes folder.
Using the upload feature in your cpanel control, upload the new Restaurant theme folder from your desktop into the themes folder on your hosting account. You will probably see a notification saying you about to overwrite the original theme, click to confirm and you’ll overwrite the original version of the Restaurant theme with the new one.