After your MOC has been submitted and approved, you can still modify its details.
On the MOC's page, you will see an Admin tab:
On that tab, you can change the image, descriptions, links, building instruction files etc. You can also disable your MOC using the Deactivate MOC button.
To modify the Inventory of parts, click the Inventory tab. Clicking on a part will display a popup where you can edit the part details. For example, clicking 6091 might show:
From the 'Edit this Inventory Part' tab you can change the part, color, quantity or delete the part.
You can also add additional parts to your MOC inventory by adding them individually or importing them from a supported file format. See Importing Parts for more details.
See Fixing MOC Errors for more details on specific problems that can occur with inventories.