With the zoom grip off, carefully pry up the macro switch cover at the lip formed in the edge where the grip was. Hold down the silver macro switch with a small screwdriver as you remove the cover so the switch and spring underneath will not be lost. The cover is usually held on by just friction on the four little pegs underneath in holes in the zoom ring. About half the lenses I've seen have some glue applied and one or two pegs will break during removal.