You can delete or cancel bookings according to the following rules:
1. Future bookings (tomorrow and beyond).
Anyone can cancel their future bookings, just left click the booking in your calendar to see the details.
In the top right you'll see the 3 dots for 'More actions'.
Click that to bring up the option to cancel.
Just to keep everyone in the loop, when you cancel your approver will be notified by email.
2. Historical bookings (today or earlier).
These bookings need to be cancelled by either your approver, or any admin user.
The process is identical to the above, find the user and date on the Wallchart, left click to see the full details and the option for 'More actions' is in the top right.