Unlike paints, you cannot ‘wallpaper’ over an old layer of wallpaper. You need to remove the old covering completely before you can paste a new layer. And this could get both messy and tiring if you don’t know how.
The first thing you need to understand is that different wall-coverings adhere to the surface differently. This means, while some coverings may come off easy, others may require a little more patience. Whichever be the covering you use, the general method of removal is the same.
A scraper will be your best friend when it comes to removing wall-coverings. Test a small area to see if the covering comes off easy. If so, remove the paper from the bottom to the top. If the adhesive is stubborn, you may need to soak the wall-covering in a solution of warm water, detergent and wallpaper paste. The latter helps retain the moisture. Do not try to scrap of stubborn coverings otherwise, as this may damage the plaster underneath. You may need to soak the area for well over half-an-hour before you can remove the covering. You could also try using a steam stripper, instead of soaking it in a manually prepared solution. Just be careful of the steam. Also if you are soaking the wall-covering, take special care around sockets and switch boards. Try to scrap off this area without water. Even if you do soak this area, switch off the main power supply as a precaution. If after stripping, you still find some patches of paper stuck to the wall, just soak it in another coat of the mixture and try scraping it off.
Wait for the walls to dry and you are all set to redecorate your walls!