If you pull them out (I know how*) they will usually crack and break the plaster and leave a big crater.
To get rid of them without damaging the plaster, so you can easily redecorate, put a longish screw against them, and tap it with a hammer. It will start to go into the hole in the plug, and will also drive the plug below the surface. Once it is 6mm or a quarter inch below the surface, remove the screw by unscrewing it, and use a fine filler to fill the hole. A wide metal filling knife, pressed hard, will give the best surface and you can use it to remove any filler lying above the level of the wall, so you will not have to scrape or sand it off later.
*If for some reason you need to get the plasplugs out, and don't mind making a crater, wind a screw in and pull it out using a claw hammer. The plug will come out and the surface will be damaged.