you asked "Hi where is layer set manager in altium 18" and I automatically read layer stack.. so sorry about that...
anyway you can acces the layer set in the PCB document (don't know if you know it)..
there used to be an option that was accessable from the PCB editor, something like creat layerset from current visable layers.. but can't find it anymore in ad18+
also in my picture go one item below the highlited one..