Start glue wallpaper should be from the window. Otherwise, the seam that you leave on the walls of the room will be too noticeable.
Rearing old wallpapers is also a rather problematic process. You can make it easier if you put a warm rag on the wallpaper, and then iron it with an iron (naturally, hot). Then the wallpaper will quickly lag behind and the pace of your repair will be significantly accelerated.