Our blades keep their edge for a reasonable time dependent on what you are cutting as they are made of tool steel. They blunt fastest when cutting board. Below are the instructions for sharpening our blades. We do also stock replacement blades. Our blades are secured by bolts which screw into threaded inserts which makes them easy to undo for sharpening.
The best way to sharpen the blade is using a water lubricated sharpening stone. The best stones are diamond coated on a metal plate and made by companies such as Eze-Lap. You sharpen the blade by removing it from the plough by undoing the screws. Place the blade flat on the stone bottom edge down, countersinks down; then move the blade in circular motions to rub away the metal from the base revealing more of the already sharpened curve. In other words don't sharpen the curved edge.
There are also Japanese water stones which will do a good job, you will need a fine one.