1) Click on "Manage Inventory" under the 'Inventory' heading of the Control Panel.

2) Search for your item by it's Item ID (or Author / Title)

3) Scroll down to the 'Search Results' and click the 'Edit' link under your item.

4) Click on the 'Amazon Properties' button.

5) On this page you can edit an individual item's Amazon properties.  You can update, change it's quantity, or remove your item from Amazon.  As you scroll down you can edit your item's Pricing, Listing, Collectible & Shipping properties.

6) When you are finished editing your item's Amazon properties, be sure to click the 'Save Properties' button to finalize.