Hi Marcia,
To enter your return policy, click "Maximize" next to the Checkout Options section of the lister page. Then, click the "Choose/Modify Return Policy" link.
If you have created a profile containing your return policy, you can edit it in your profile by going to Auctiva -> Profiles(tab) -> Manage Profiles, and selecting "Edit" from the pull down menu to the right of the appropriate profile.
-Mike