Tech support helped me out. Once you upload the Hypermodel,you download onto the free BIMx viewer. Once you open it, viewer will tell you you need the PRO version. You buy it for that specific Hypermodel. You will get the opportunity to add others to the email list; they receive a link to the HM. The email with the link only comes once, so be sure to save it. It's a $50 link. You can distribute the link to as many people as you want. When updating, be sure to name the new HM the same as the original; the link is good only to that specifically named project.
Now I'm going to try it.