Using the left navigation menu, go to > Setup > Services > press the '...' button beside the service that needs to be delete > Delete
It is recommended that you deactivate the service instead of deleting it as this will allow you to reinstate it in the future if needed. This option will not allow you to book manually on the back-end Calendar.
If you wish to stop offering a service, you can also change the offer end date to the date you wish to stop the service from.
You can do this by going into the Edit section of service > General tab. (Please see article below)