Can't update Hazel 5.1.1?

I just installed Hazel on a shiny new Mac Mini -- and noticed that on my old MacBook the old version 5.1.1 is installed.
When I now try to update on the MacBook via the "Check for Updates" menu entry no update info gets shown, just the menu entry ("Check for Updates") bbecomes greyed out.
What's going wrong?
When I now try to update on the MacBook via the "Check for Updates" menu entry no update info gets shown, just the menu entry ("Check for Updates") bbecomes greyed out.
What's going wrong?