Once you have logged into your control panel, click onto the "Websites & Domains" tab.
You will then select "Backup Manager" from the icons on this page:
Now click onto the button "Backup":
Now fill out the "Backup Settings" form as shown circled in red below:
Once the backup has completed, you can download the backup from your "Backup Manager" page. Just click on the "Save" icon beside the backup that you wish to download.