Put a cloth around the shank of the ratchet in a vice, lever off the handle.
The for the screwdriver, find a socket that's end matches the size of the round "cut" around where the shank goes in. (This prevents damage to the handle during removal) then put a cloth around the shank and clamp it in a vice. Use a prybar between the vice jaws an a socket and lever off the handle. (make sure the bolster will pass through the socket).
the ratchet handle part that goes into the hard handle has a step in it. Drill out the new hard handle out to the diameter of the end of the shank for the length of the ratchet handle that goes into the hard handle. Then drill out the wider part.
The ratchet handle has "wings" on it, to stop the hard handle coming loose or spinning. Fold up a cloth and put it on a hard surface, put the ratchet head on it, line up the hard handle and hit it with a soft-faced dead-blow hammer.
Job done.