How do I renew all library materials at once?

On the Checked Out page click the checkbox next to the item(s) you wish to renew (or you can click "Select X items" checkbox to renew all items).

Then, at the bottom, click on the Manage Items button and select the Renew Items link.

You may have items that are not able to be renewed (e.g. on hold for someone else); you'll see a notice for that at the top of the page.