Inspect the wood balusters to see how they are installed into the handrail and the floor. They may be toe-nailed, screwed or have a dowel that fits into a hole in the floor.
Cut the wood balusters in the middle and remove the top pieces using a reciprocating saw or hand saw.
Remove the bottom; exactly how you will do this depends on how they were installed. If they don't seem to come up and aren't dovetailed (as they are in older homes), try rotating counter-clockwise as they may be screwed into the floor.
Measure the top of the metal balusters to find how large its area. Most metal balusters are square, so you'll probably have a 1/2-inch-square baluster or something similar. You'll need this measurement when installing them into the handrail. If the top tip of the baluster is turned -- rounded -- measure its diameter. These turned tips allow you to install the baluster in a round hole without needing a shoe to cover the hole.
Ensure the holes are at least one and a half times larger than the measurement across the tip of the baluster.
Drill the first hole into the bottom of the handrail at least 1 1/2 inches deep and test-fit one baluster to make sure it fits before drilling all the holes.
Drill holes in the floor the same diameter as you did in the handrail, but only 5/8- to 3/4-inch deep.
Measure the space in between the bottom of the handrail and the top of the floor. Cut the first metal baluster to 1 3/8 to 1 1/2 inches longer than this measurement using a chop saw, band saw or grinder with a metal-cutting blade. The balusters need this extra length to fit properly into the handrail and the floor.
Test-fit the first baluster into the handrail and the floor to make sure the fit is perfect. If so, continue cutting the other balusters; if not, remeasure and cut until it fits properly.
Slide the shoes onto the balusters and fit the balusters into the holes. The shoes are decorative adornments that go over the bottom of the baluster and hide the round hole in which the square baluster sits. Tape the shoes in place with painter's tape midway up the baluster and install the baluster with a special epoxy or subfloor glue designed for metal and metal-to-wood applications. For the shoes, apply a small amount of the epoxy or glue around the bottom part of the baluster and slide the shoe into place.
Allow the epoxy or glue to cure for the recommended time -- do not disturb the balusters during this time or you may interfere with the curing process.