Wtf, I KNOW I replied to this earlier. Friggin' forum glitches -_-'
Anyways, on the X3 theme, it's under Files right next to Backup Wizard, Legacy File Manager and File Manager.
Should that not work:
http://yoursubdomainhere:2082/frontend/x3/backup/index.html
Where yoursubdomainhere is something like thisismyaccount.x10hosting.com . Pulled the link outta my cpanel, hope thats what you're looking for
Quick note too, some ftp programs have backup controls in them. They basically just view the folder structure and download every file in every folder (preserving the tree, so it'll make a subfolder if it needs to). When it comes time to, you usually just tell it to upload the contents of the backup folder and it'll replace everything
On X10 it might be best if you only backed up the public_html or www folder though, dunno how much of the other folders we can screw up (I'd hate to have to remake an account)