If you have a backup of your website in a compressed archive such as: zip, tar, tar.gz, tar.bz2, tar.xz, tar.lz4 or tar.sz and it's less than 100GB, you can easily upload it using the File Manager!
Just go to Websites → Manage on your panel, search for File Manager on the left sidebar and click on it:
Once there, select the Upload button in the upper right corner:
There you will be able to choose a file (archive for example) or a folder:
That's it! Now you know how to upload a backup with File Manager 😊
To upload larger files, follow this guide: How to upload backups with FTP