First, click on the “Edit” button to edit the event you would like to modify. Then scroll down to the “Ticket Pricing and Options” section and click the “Options” button for the ticket you would like to hide or mark as sold out.
After this you will see a number of options letting your change the status of that particular ticket type. Click on the one you require, and then press “Update Options”. This will only affect that one ticket type so you can continue to sell your other tickets normally.