For small and medium-sized magnets, the operator can separate them by sliding the end of the magnet off the stack by hand.
For medium and large magnets, they can often be separated by using the edge of a table or countertop which is usually perpendicular to the magnetisation direction.
Here is the detailed how-to:
For very large magnets (generally 50.8mm / 2inch and larger), a specially-made magnet separating tool is required as the picture below. You'd better ask a specialist to help y ou with this. Do NOT do this if you never did it before.