The below process will walk you how to generate a back up on of your account.
Step 1: Log into your cPanel account (click here for How to sign into cPanel)
Step 2: Click on "Backup"
Step 3: Click on "Download a full Website Backup"
Step 4: Click on "Generate Backup"
Step 5: You should now have a blue box telling you the backup is in progress, Click "Go Back"
Step 6: Refresh this page until the backup up link under "Backups Available for Download" turns blue.
Step 7: You will get a prompt to download the file. Select "Save File" and click "OK"
Once you have a copy of the back up on your computer please read "Removing old cPanel Backups"