First login to the agent's account and then click View Listings or View/Edit Listings.
Next, find the appropriate listing and click the green text code button.
Then, click the orange Remove Existing Keyword from Listing button.
Upon successful removal, you should see the following message: Removed Existing Keyword from Listing!
Next, click the View Listings tab to go back to your listings page.
Then find the appropriate green Text Code button in the right-most column of the listing to which you would like to attach the keyword.
Next, click Suggest Number and locate the keyword in the two drop-down menus.
Select the newly released code and click Use This Number.
Then click Save Key Code.