First of all, it is necessary to remove the old wallpaper or plaster from the walls. To do this, the surface of the wall should be moistened with water, for more convenience you can use a soft roller. Wet wallpaper will move much easier. On top of the old wallpaper, new ones cannot be glued for several reasons: firstly, the old wallpaper may simply not withstand new weight and will peel off, and secondly, if there is a bright pattern on old wallpaper, it can manifest itself through new ones, thereby reducing all efforts to zero to zero.