You have the ability to void tickets, making them unusable, right from the transactions page.
If you don't know the specific event, go to the general Transactions page on your dashboard pop-out menu
However if you do know the event, you can go to the event specific transactions page
On the left hand side, you will have multiple options to help you filter and find the transaction that you are looking for
Once the transactions is found, select the gear box in the bottom left hand corner and choose Void
Void All is the default selection and if you'd like to void all of the tickets in a transaction you will only need to select void when the pop-up screen opens
If you'd only like to void select tickets, you will need to unselect Void All and choose Void Selected Tickets. From there, you will be able to choose which tickets to void
A new transaction will show up on your transactions page showcasing the voids that were made
Please note: A ticket that is void does not mean that it has been refunded