This article relates to version 4 of myPractice and version 5 of Bp Allied. All Documentation links relate to version 4 but the same principles apply in V5.
It's not possible to delete a practitioner within myPractice as practitioner details are attached to historical records within the system. It is possible to disable the practitioner to make them inactive. This will retain all of their past records and remove their name from the login screen as well as their calendar.
See the Article on How to disable a Practitioner.