Assuming 4.x, licenses are connection based. A user who connects to a resource ie drive mapping, consumes a license. The number of user objects in your tree is irrelevant. You could have 1000 users in your tree and a 100 user license on your server. Only 100 (max) users could connect. The other 900 would have to wait for a free connection. Just delete the user (should disable for a week or so then delete).