Set up your scaffolding directly below the fascia boards you need to replace. You can perform this task with a ladder instead, but using scaffolding will save you a lot of time.
Remove the screws that hold your gutters to the fascia board. Pull the gutter away from the house and lower it to the ground. If the gutter section contains a downspout that is screwed into your house, remove these screws first. Be careful when you lower the gutter to the ground, as you want to be able to reuse it.
Drag your utility knife along the joint where the fascia meets the soffit. There is usually a bead of caulk here that you need to sever.
Insert your pry bar between the fascia and the soffit. Push the loose end of the bar toward your home to pry the two pieces apart. Repeat this process along the entire length of the fascia, then pull it away from the house to remove it.
Place the old fascia board over a similarly sized replacement board. Trace the outline of the old board onto the new one, then cut the new one to fit.
Clean out any debris resting on top of the soffit while you have the fascia removed. Make small marks on the underside of the soffit wherever the rafter tails or lookouts are located, so you will know where to nail the new fascia board into place.
Place the new fascia board onto the side of your house. Drive three 3-inch galvanized steel nails through the fascia and into each rafter tail or lookout.
Apply a bead of caulk between the new fascia board and the soffit. Wipe the bead with your finger to ensure it is completely securing the gap between the boards.