What steps does my company need to take if a customer wants an exchange, refund, or cancellation of an order after it has been processed and payment has been made?

It depends on the exchange/refund/cancellation policies that you set forth for your business.  

If you allow exchanges, you simply confirm the customer's request for an exchange, and update the status of their order to processing.  Follow these steps to process an exchange for a customer's order after it has been completed and payment has been made: Login to your account, click the “My Account” link in the top right, then select the “My Business Orders” tab.  Choose the customer's order from the list; if you have too many orders in your list, you may limit the items displayed to only reflect orders that are in the processing stage by selecting “processing” from the order status dropdown in the search box and selecting “apply”. Once you're on the order details page, click the “Edit” tab, change the status of the order from completed to processing, add a note to the customer about the exchange, then click the “Save” button.  Next, complete the necessary exchange with the customer and then update the status of their order to completed.

If you allow refunds/cancellations, you simply confirm the customer's intent to cancel, refund any monies, if applicable, and update the status their order to cancelled.  Follow these steps to process an cancellation/refund for a customer's order after it has been completed and payment has been made: Login to your account, click the “My Account” link in the top right, then select the “My Business Orders” tab.  Choose the customer's order from the list; if you have too many orders in your list, you may limit the items displayed to only reflect orders that are in the processing stage by selecting “processing” from the order status dropdown in the search box and selecting “apply”. Once you're on the order details page, click the “Edit” tab, change the status of the order from completed to processing, add a note to the customer about the cancellation/refund, then click the “Save” button. Next, complete the necessary cancellation, refund an monies to the customer and then update the status of their order to completed.