OK, I should also have noticed it was in the avast! Server Protection sub-forum.
I believe the same is correct if you have a valid license you should be able to convert it for the remainder of the period.
There is a convert link for the stand alone avast versions, but I don't know if there is a similar one for the avast! server version. So I would suggest contacting sales (at) avast (dot) com about conversion of the license.