If the organizer allows it, you can upload products from the Exhibitor Center. The limit number depends on the organizer's restrictions.
To add images and link them to your products just click on the "+" icon and upload a file 400x400px (1:1 ratio) 1MB max.
Once you have uploaded all the images related to your product and filling out the rest of the fields (name, description, custom fields), you can choose the thumbnail image by clicking on the star icon.
You can change the thumbnail as many times as necessary by clicking on the star icon under the image you want to use as the main view for your product.