get on a lader and break the sheets loose form the top first. Go down behing the sheeting with a crow bar and pull the sheet from the top while prying on the studs with the crowbar. Anyway you do it if you are trying to save some wood is gonn abe slow though. Man.....That hardi plank is some aggrivatong stuff to put up. especially on from a high walkboard. Forget driving a hand nail through it unless you predrill first. Nail it with the nail gun but practice on a few small peices to get the pressure set right first.
Esab Migmaster 250 w/ ST23-A Spoolgun
MIller Bobcat 225
Miller Syncrowave 200
Hobart Handler 120