Every effort has been made to ensure that version 2.0 is backwards compatible with earlier versions. If you run into issues, most likely it would be because of further customization you’ve done on your site.
As with any other plugin update, please test the Image Intense update on a staging/development/test site before updating your live/production site!! You might have custom CSS that is now handled by Image Intense. Always, always test any updates (not just Image Intense) on a development or staging environment. Never do updates to a live site! If it turns out something isn’t working right in your testing area and you can’t figure it out, get in touch with us.
In fact, if your current Image Intense modules are working like you want them to, we would suggest leaving them alone. There is no security need to update. You can use version 2 of Image Intense on your new sites or when upgrading your current sites.