Hold an iron over the seam for a few seconds to heat the old seam tape adhesive underneath.
Place a straight edge over the seams and remove about an inch of the old carpet. Run a utility knife along the straight edge to make the cut as smooth as possible.
Place a knee kicker near the seam and hit it with you knee. Wear knee pads to prevent bruising. Stretch the carpet to make up for the lost inch that you cut away.
Cut a piece of seam tape the length of the seam using a pair of scissors.
Put down the piece of seam tape underneath the carpet seam so that the tape is half way between the two pieces of carpet.
Heat the tape using an iron and press the carpet down on to the tape. Set a heavy book on top of the seam to keep it from stretching back.