the facia boards on my home are old, warped and in need of replacement. the roof was originally a rock roof with the deeper flashing withnthe raised edge to retain the rock. it has been overlaid with asphalt shingles but the old flashing is still there. i would like to replace the facia boards but how do, i get the old flashing up without ruining the shingles that are at present in good condition? the flashing is of course nailed on under the first course of roofing.