Replacement of executors after grant

We are a Ltd Co Solicitors practice where three or four clients who have now died Wills have appointed directors as executors and expressed the wish that only 2 act in the administration of the estate.
Grants of probate have been obtained on these matters in the names of 2 directors. One of the directors is now retiring from the practice and I am looking for some pointers as to the correct procedure to remove that retiring director from the grant and appoint one of the other directors to be the second executor

I have looked at this in the past and it is extremely difficult, necessitating a Court application (and that was just adding, not retiring).

I suspect in 99% of cases it is easier to leave it as is - perhaps with the “retiring” executor delegating powers or granting a POA where that is possible.