Delete referencing assets

Hey there!

I am creating an architectural project in UE4 and faced the problem I can not deal with.

As I remember, initially I was working in file “Test” and than saved it under the other name “House” und continued working for some weeks. Suddenly I discovered that I can’t delete assets in that way like before (see screenshot 1).

I was trying to solve this problem alone and found out, that I have 2 levels named “Test” and “House”, that somehow referencing each other. (see pict. 2,3).

Truly I don’t have any idea about the sructure of this and I would be very thankfull if somebody explains me how to weld this two levels in one or to solve the problem with deleting…because if I replace one of two levels half of my project disapears.