I am in a similar situation and haven't found anything else close to asking or answering this question, and this has been sitting for over a year without any response.
I assigned a user read-only permissions by mistake, and cannot see any way to update their folder permissions to increase the level of access. In fact, I don't see any way to edit or remove permissions once granted. Am I just missing something???
Do I have to remove and re-add the user completely to change their permissions on a given resource?