To access your Inventory controls, click Products in the menu on the left then click Edit next to the Product with inventory to be updated.
From there, click the Manage Inventory button under the Inventory section to access your inventory settings:
To update your inventory, enter the Quantities available in the Quantity fields provided then click Save.
Check the box under "Infinite" should a particular inventory item be unlimited or not limited to a specific supply number.
In addition, you can set specific SKU Codes, Pricing and a Quantity Alert to alert you when quantities are low.