Consult the ladder packaging to find its dimensions, both folded and extended. Choose a position in the room below the attic that will allow you to fully extend the ladder and access it. Use a stud finder to locate the ceiling joists and pencil the coordinates of the necessary hole, positioning it between the joists.
Bore small holes in the ceiling at the four corners and insert dowels up through them, allowing you to see the entry location from inside the attic. Enter the attic by its preexisting access point and examine the future location of the ladder. If the location is inconvenient or intersects electric wiring, consider installing the ladder elsewhere. Clear away any insulation from the ladder area.
Cut through the ceiling along the penciled lines, using the wallboard saw. Screw 2-by-4-inch headers into place between the joists at either end of the hole for support, then saw off any wooden braces that extend across the hole.
Set the ladder into position from the attic side. Place wood shims between the ladder frame and the joists to secure in place. Drive screws through the ladder frame, shims and joists to secure the unit. Extend the ladder and trim off the bottom end, if it is too long for your ceiling height.