To change your domain's hosting account, find your domain from the domain group and click on Actions. Then in the Hosting section click on "Modify". A popup will appear from where you are able to choose the new hosting account. Click on "Change" to change your domain's hosting account.
Please keep in mind that changing your domain's hosting account will not move your website's files, folders and databases. You will need to transfer them manually by yourself. Unfortunately, it is not possible to transfer individual domains between cPanel accounts.