How to re-assign license to another person

I have a situation which occurs often; someone leaves and I want to re-assign their license to the new person. However I do NOT want to delete the old account since I want to keep all files already created and existing under the old account. I want the new person to receive all those files.

How do I do that?

I am looking for a way to re-assign an account without destroying all data associated with it?

Thanks