What is the legal way to expel diplomats from a country under the Vienna convention?

Question

Suppose a receiving State wants to expel diplomats representing the sending State.

My question is, what is the legal method of expelling a diplomat; in case the sending State refuses to comply with the request?
Can they deport the person in some sense, or revoke the diplomatic immunity?

Relevant articles from the Vienna Convention on Diplomatic Relations, 1961 are mentioned below.

9.1 The receiving State may at any time and without having to explain its decision, notify the sending State that the head of the mission or any member of the diplomatic staff of the mission is persona non grata or that any other member of the staff of the mission is not acceptable. In any such case, the sending State shall, as appropriate, either recall the person concerned or terminate his functions with the mission. A person may be declared non grata or not acceptable before arriving in the territory of the receiving State.

11.1 In the absence of specific agreement as to the size of the mission, the receiving State may require that the size of a mission be kept within limits considered by it to be reasonable and normal, having regard to circumstances and conditions in the receiving State and to the needs of the particular mission.

Answer 1

Article 39(2):

When the functions of a person enjoying privileges and immunities have come to an end, such privileges and immunities shall normally cease at the moment when he leaves the country, or on expiry of a reasonable period in which to do so, but shall subsist until that time, even in case of armed conflict. However, with respect to acts performed by such a person in the exercise of his functions as a member of the mission, immunity shall continue to subsist.

The receiving state has to give the diplomat a reasonable chance to leave, which will normally be specified in the persona non grata (PNG) notification. If the now-former diplomat refuses to leave, the receiving state can revoke immunity. They can’t punish for stuff done as part of their diplomatic role, but they can punish for any further crimes and can also deport the person.