You can Delete your transactions from the Transactions List or by opening a transaction.
In the transaction list, when you hover your cursor over a transaction, the Colored Category icon will change to a circled checkbox. You can select that checkbox to mark the transaction for delete. When atleast one transaction is checked, the delete button becomes visible.
When you open a transaction, you can click on the delete button to delete the transaction. There will be a prompt before you can delete the transaction.