Sorry prismbeer. Even administrators on SambaPOS can't alter paid (closed) tickets. You can record refunds on Cash so your cash report will generate correct numbers and you'll be able to track refunds. If you'll be able to delete items from old tickets nobody will know that refund. We assume it a security issue.
Click "Find Ticket" button on menu numerator to display ticket explorer. You'll be able to display & print old tickets and filter them by account & table.
Hint: If you are using "table view" as default screen, click "Close" button to display menu numerator.