Yes, you just need to click Edit Transaction and make your changes.
When tickets and/or products are changed/added to the basket, this change will apply immediately.
When a Delivery Method or Customer Details are changed, you just need to click Continue and then that change will be saved.
You can then either leave the page or click Finish Editing Transaction on the final page.
NOTE - Reservations will remain in Reservation status (i.e. instead of In Basket) even if they're being edited.
Because means that Reservations will never expire when being edited, i.e. will not auto-release. This is to enable Reservations to work for Merge Tags in Templates and so that they appear in Reports.
If you would like to manually remove a Reservation, then click Clear Basket when editing the transaction.