Secure the Ulu on a table with a clamp. The ulu should lie on the flat surface with the edge of its blade extending beyond the side of the table. The handle will get in the way, so it needs to be held down firmly too.
Run the sharpener up and down the length of the blade. You can use either a whetstone or a diamond-coated steel as a sharpener. Start out gently and keep the pace until you get used to the awkward angle required for sharpening the clamped blade.
Sharpen the blade by moving the sharpener along the blunted cut. Ulu blades are sharpened in one direction along the blade when they are manufactured. Make sure to follow this direction while sharpening the blade. Keep moving the sharpener along the blade until the face of the blade looks shiny and is sharp to touch.
Turn the ulu on its other side to sharpen the other edge of the blade. You will have to place it down on another side of the table and clamp the knife in place before you start sharpening again.