To upload a backup, open Hosting → Manage → Import Website section:
Once there, all you will need to do is select .zip, .tar, or .gz archive with your website files and it will be automatically extracted to your public_html folder:
NOTES:
The maximum allowed size for uploading a file using this feature is 256MB
If you want to upload a bigger file, you can use an FTP client or File Manager (Beta)