In looking at the other replies, nobody addresses how you will touch up the unstained parts after you get out the old balusters or how you will get the iron ones installed with the carpet. "Treeoflifestairs.com" does bring up some of these concerns. As Steve Neul says, if you don't plan on keeping the old balusters, cut them in half and gently wiggle them out. There might be some glue and nails in the ends, but if you gently wiggle them out, you won't cause much damage. That still leaves you with a lot of stain touch up and figuring out how to install the iron ones. If you don't have experience or tools for the job, you are in for a ride.
My advice, call "Treeoflifestairs.com" and have them install the railings.