If the house is built the way most are today using platform framing, it isn't going to be easy whether you do it yourself or you hire someone. You will have insulation in the exterior wall. To get from the attic to the first floor, you will have to go through the top plate of the second floor wall, a fire stop about half way down, the bottom plate, the top plate of the first floor wall, and possibly another fire stop depending on where you want the cables to come out of the wall. If that is what you have, it will probably require opening the wall.
An alternative is go straight through the wall and run conduit on the outside.
If you have an old house with balloon framing, no insulation and no fire stops, it is a snap.