How Can I Be Removed From A Shift?

During your shift you can mark yourself as unavailable to stop receiving calls. If you want to do anything more it depends on your access level. 

If You Are An Organization Administrator:

Then you are authorized to make this change.  In fact, you can make any change you want to your organization's schedule (including to your shifts, or anyone else's shifts in both the past and future), even last minute, by just going to the modify schedule tab.

If You Are Not An Organization Administrator:

Then you are authorized to make this change. You can't remove yourself or anyone else from a shift. Your only option is to reach out to an organization administrator and request they make the change for you.