Measure the area for the entryway, and mark the corners of the carpet by dabbing them with a marker.
Make a line on the carpet by snapping a chalk line from one mark to the next around the perimeter.
Place a T-square up against the wall, and align the longer part of the T-square with the chalk line. When the T-square is butted up against the wall, the longer part of the T-square should align perfectly with the chalk line. This is an easy way to make sure your line is square. If the two don't line up, measure again and mark a new chalk line.
Cut the carpet along the line, using a utility knife. Apply moderate pressure to the knife, and cut slowly so you stay on the line and get a good cut.
Pull up on the corner of the carpet that is farthest from the wall. If the carpet does not easily come up, jiggle it to release it from the floor. Depending on how the carpet was installed, it will either be held down with glue, staples or carpet tack. Pull back on the carpet until the entire piece is loose. If it is held down by carpet tack, you'll need to jiggle the carpet along the perimeter to release it from the tack's teeth.
Pull up on the carpet pad to remove it from the floor. In some instances, the carpet and pad come as one piece, so the pad would have been removed at the same time as the carpet.