Click on the Configuration menu on the left hand side of the screen.
Click on Manage Sales Channels.
Click on the eye icon on the right hand side of the screen.
Click on the trash bin icon on the right hand side of the pop-up.
A popup will appear just to ask if you confirm that you want to delete the marketplace, press "OK" if you do or if you have changed your mind press "Cancel".
Congratulations you have deleted a MarketPlace .