In the rule entitled “Dungeon” replace the text

If the attempt is successful, and their Dungeon Level is less than the Amulet of Yendor’s, they increase their Dungeon Level by 1. If the attempt is successful and they have the same Dungeon Level as the Amulet of Yendor and no @ has an Amulet of Yendor in their Inventory, they add the Amulet of Yendor to their Inventory. If the attempt is successful, and either their Dungeon Level is greater than the Amulet of Yendor’s or they have the Amulet of Yendor in their Inventory, they decrease their Dungeon Level by 1.

with

If the attempt is successful, they increase or decrease (their choice) their Dungeon Level by 1. If the attempt is successful and they have the same Dungeon Level as the Amulet of Yendor and no @ has an Amulet of Yendor in their Inventory, they may instead add the Amulet of Yendor to their Inventory. If an @ successfully Finds the Stairs when their Dungeon Level is 1, they may not choose to decrease their Dungeon Level by 1, unless the Amulet of Yendor is in their inventory.