UND has a subscription with Zotero that provides everyone who registers for Zotero with an @und.edu address with unlimited cloud storage with Zotero. All you have to do is use your @und.edu address as your primary email address and unlimited storage will apply automatically. If you registered with a different email address, you can add your UND address to your profile page on your Zotero account settings.
If you have any further questions, feel free to reach out to your subject librarian.