How To Texture Over Wallpaper?

If you have (paper) wallpaper you can't texture over it because the wallpaper will start to peel up and let go of the wall once moisture from the texture is applied to it.
  Best to go ahead and pull the paper off. If the back layer of the paper is still on the wall, you can fill a sprayer with hot water, spray it down and let it sit for a couple of minutes, then take a putty knife and scrape it off.
  If you have vinyl wallpaper, there is a good chance that the texture will not stick to the vinyl paper and may start coming off over a short period of time once the texture has dried.
  You could apply a primer over top of vinyl paper before texturing, but I don't recommend you do that because wallpaper will sometimes let go of the wall over time. Especially if it is in a moist environment or heaven forbid, you get a leak in your roof at some point.
  Recommend you go ahead and remove the wallpaper before texturing to be safe, because if any of these problems occur, you are going to have a mess to deal with.
  Removing the wallpaper isn't really that difficult as long as you remove that top layer first, then wet the backing that is still on the wall. Most of it will peel off in large sheets. Just remember to let the dampened wall sit for about 2 minutes before peeling off, but don't let it sit too long because it will dry back up and you will have to re-wet it.
  Hope I have explained this well enough for you.
   If you run into any problems or have any questions, leave me a comment.

First you need to know if the wallpaper is on securely or youre going to have fun later then using a roller and water downed sheetrock mud, roll on your texture