You must be logged in as an MSP Admin user to make these changes.
To Delete an Admin account the user must first be demoted to an MSP User.
Within the SaaS Alerts UI open Settings -> Users and then access the row of the user you wish to modify and click the edit pencil:
Then unselect the check box next to MSP Admin and click Save:
The above steps may also be used to promote an MSP User to an MSP Admin
Now that the user is no longer an MSP Admin the Trash Can icon to the right of their name on the user row will allow them to be deleted.