@bayside You can manage through CPanel of your hosting account; from Hosted domain choose domain which you want to remove and then click on Remove. (Steps may be different depend on your hosting provider panel)
I advise before remove, better to take backup of your source, database for future reference.
P.S - Think twice before action, you might be get good profit by upgrading site / business. Good luck
Cheers 
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Magento Programmer | Was my answer helpful? You can accept it as a solution.