wall paper with the new one. Because there is one difference. It is recommended that you brush glue directly on the new wall, but never apply the glue on the old wall papers. I did it long time ago when I was young, poor and had lots of time on hand. It will be quite a job depending on how large your room is and how smooth your walls are. You may need to sand down the lumps on the walls and make the walls as smooth as possible.
Have fun.