Re: Orange peal to knockdown
It would be easy enough to float over the orange peel to smooth it out, then respray a knockdown texture. Float with topping compound and then you can either buy dry mix texture OR you can simply wet down more topping compound to a pancake batter consistency and spray that. IMHO, if you are not well versed in drywall, using topping compound for texture will be the easiest.
The reason you float to a relatively smooth surface is so that the new texture has a flat surface to stand out from. It doesn't have to be perfectly smooth, just not a real visible texture. You can sponge or lightly sand to remove trowel marks before retexturing.
Assuming that you are doing the work yourself, you will want to rent a texture gun. Do some test shots to get the hang of handling the gun and to set the size of the texture blobs. Once you're ready, go ahead and start spraying. Let the texture just start to crust over, then you knock it down with a drywall knife.
Again, practice will help you get the hang of using the gun as well as when and how to knock down the texture. The easiest way to do this will be on a piece of plywood or even the garage floor. Once you're happy with your ability, move inside to the ceiling.
More tips available if you need them.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!