How can I edit or delete themes in Zoho Campaigns?

Zoho Campaigns lets you edit the theme of the campaign while drafting the email content using the footer component in the template editor. You can't create, edit, or delete themes under Settings anymore.

However, you can use the existing themes that you've already created. Hover over the theme and click Set as default link. You can view other users' themes but you cannot set those as default.