Hmmm..... front wheel is off, but axle is still in? Must be one of those forks that clamp the axle?
Anyway, remove the axle nut if not already done.
Tap axle out of hub. Use a block of wood or a plastic mallet to avoid damaging the axle threads. Or, loosely screw the axle nut back on flush with the end of the axle and tap with an ordinary hammer on the nut itself. This will allow you to not damage the threads, but obviously will not let the axle all the way out.
Once the axle is out, the brake backing assembly (or, 'drum cover') falls out of the hub. Or, if the brake / hub / shoes are very badly corroded, they may all be stuck together. Persuade as necessary per your favorite method.
Replacement of the shoes will then be obvious.