cPanel offers a feature that allows you to convert an addon domain to a new account.
This process is irreversible, although if you create a backup of the original account beforehand, you could terminate the newly created account and then restore your previous backup to revert the process.
1. Login to WHM as the root user
2. Navigate to: Home »Transfers »Convert Addon Domain to Account
3. Click the "convert" button for the domain that you would like to convert to an account
4. Select your desired configurations for the new account
5. Scroll to the bottom of the page and click the blue "Start Conversion" button