How to Remove or Allow the Ability for Requesters to Adjust Catalog Items within an Order

Goal:

Under the Procure tab, select Product Catalog.
Select the button beside the Catalog Item you would like to make changes to.
Select Edit Item.
In the bottom left-hand corner of the new window, use the Catalock toggle button to allow the items to be editable or uneditable by Requesters.

For information on making these changes to all Catalog Items take a look at How to Manage the "Catalock" Permission for All Product Catalog Items.