Place the cordless drill in reverse mode to unscrew the screws currently holding the shelf in place. Remove the screws one by one until you can remove the shelf and shelving brackets off the wall. Separate the shelf from the brackets using the drill in reverse mode.
Use the wall stud finder to locate wall studs. Slide it across the wall, and make a small pencil mark when the device locates a stud. You need at least two studs within the width of the shelf frame. Place the shelf frame up to the wall with the level on top of it. Keep moving it until it is evenly placed on the wall. Use the cordless drill to drill 3-inch screws through the frame into the wall to mount it.
Hold the shelf up to the poles sticking out, so it is horizontally placed the way you wish to hang it. Determine where you need to drill the holes to insert the shelf on the poles. Make two pencil marks to indicate the locations. In addition, determine how deep the holes need to be.
Drill the holes into the shelf's side on one of the length sides. If the poles are long, use the extension drill bit. Slide the shelf onto the poles when the drilling is complete.