Gain access to the roof by way of a ladder or scaffolding.
Wedge a pry bar into the line between the plywood sheets or planks. Pull the pry bar toward yourself to lift the edge of the plywood or plank. Move the pry bar down the length of the plank or sheets and continue to pry up the sheathing. Begin the removal process at the roof peak so you will always have a secure place to stand or kneel.
Remove the pry bar and tap the wood plank or plywood sheet back in place with a hammer using care so as not to strike the nail heads. This action will pop the nail heads and leave them loose.
Insert the claw end of a hammer or claw end of the pry bar under the nail head and press the handle of the hammer or pry bar down to force the nail out of place. If you are unable to wedge the claw under the nail head, position a nail puller at a low angle to the nail head. Strike the nail puller with a hammer to fit the end of the nail puller under the nail head.
Continue to alternate between lifting the sheathing, tapping it back in place and pulling nails. Work your way across the roof from the peak and move down toward the eaves until you remove all sheathing.
Move the ladder or scaffolding to the other side of the house to gain access to the sheathing on the opposite side of the peak. Repeat the same techniques to remove the second half of the sheathing from the roof.