Drill From 1st Floor To Second Floor
If you are unsure of what may or may not be inside the wall it is necessary to open up small inspection holes in the wall. Holes 4" x 4" are typically used for this purpose. If your wall surfaces are drywall or sheet rock that is a good thing because it is relatively easy to patch up these holes, particularly if you keep the cut out piece to be used for the patch.

Sometimes when running conduit or wires from floor to floor it is necessary to open up slightly larger holes (maybe 4" x 6") near the floor and the ceiling to gain access for drilling the necessary holes and shoving the conduit/wires through. 

There are numerous questions here that address the process for patching these access and inspection holes.