Once the siding has been removed, fold back the building paper to gains access to the plywood underneath. If working in sections, the building paper may be cut vertically. The paper can be taped to the wall higher up to keep it out of the way.
With the paper out of the way, remove the nails holding any cladding to the plywood using a nail puller. Mine is designed to be driven under a nail head with a hammer. These nails are typically hidden under the siding, so it is less important not to make a mess of them.
Then make a horizontal through the plywood sheet. Sheets are typically 8ft high by 4ft wide, so the sheet may be cut the entire 4ft width. Set the circular saw depth to just more than the thickness of the plywood - it is important not to cut into the underlying studs which would weaken them.
Once the plywood sheet is cut, use the nail puller and claw hammer to remove all the securing nails. Then remove the cut section, exposing the sill plate.