Log into your account. At the top of the page, click "Account", then click on the "Gallery" tab. From there, click "Manage Images In Portfolios".
In the portfolio management screen, click on "Manage Images" for the "Archived Artwork" portfolio. Click the checkbox for each image you'd like to add Archive, and then click the "Add Images" button.
Alternatively, you can click the "Remove Image" checkboxes at the top of the screen, and then the "Remove Images" button, to unarchive images.
This is available to 3 Star and 5 Star accounts only.