Move furniture out of the room that has the lumpy carpet.
Loosen the carpet at a corner in the room. Pull up on the carpet carefully using pliers. Once started, pull up the carpet from around all the edges in the room.
Roll back the carpet along one wall. Remove the tack strip by pushing a pry bar underneath it. Pull up to remove the tack strip.
Measure and cut a new tack strip for one wall. Use a tape measure and saw to complete this process. Hammer the tack into place using the small nails attached to the tack strip.
Follow this same process to install new tack strips around the entire room.
Flatten the carpet in the room, making sure that the carpet covers the new tack strips.
Attach the carpet along one wall using a knee kicker. Lay a power stretcher onto the floor and attach one end along the wall where you used the knee kicker. Place the other end at the opposite wall.
Stretch the carpet in a fan pattern, work from the inside out. Use a knee kicker to attach the carpet to the tack strips along the wall.
Complete these steps on the remaining two walls in the room.
Cut excess carpet from around the walls using a utility knife. Push the carpet beneath the baseboard with a carpet tool.
Replace the furniture.