Dave, you don't need to empty the system; just bleed it as usual, but keep filling up and continuing till you have clean fresh fluid pouring through. I use a bleed easy kit from Halfords to do mine, which is really simple. I was always instructed to start with the wheel farthest away from the master cylinder, in your case the rear nearside, then the rear of side, front nearside, and front of side. Best wishes.