Measure the width and height of the doorway opening, and trim the bifold door to fit the opening if it's slightly too wide or tall. To trim the door, use a plane along the outer edges of the door. Position the plane at one end of the door, and draw the plane across the door edge, applying a slight amount of pressure to the front of the plane.
Center and install the upper track for the bifold door on the top doorjamb board. If you are using only one bifold door for the opening, ensure that you install the pivot point on the track on the side you want the door to pivot on. Screw the track into place using the screws provided with the track.
Dangle a plumb bob from the center of the track 1 1/2 inches out from the wall, and have an assistant mark the point on the floor that the pointed tip of the bob indicates once it comes to rest.
Center the bottom pivot over the mark you made, and install it according to the manufacturer's instructions. Attach some pivots to the floor, and attach others to the wall.
Set the door into the bottom pivot first, depress the top pivot with your fingers and align the door so the pivot is in the track before releasing the pivot. Straighten the door up until the pivot snaps into the depression in the track.