Change Virtuemart Checkout appeareance

Hi,
Please Help me to change the way that the customer make the check out in my store. I want when custumers proceed the purchase, the page force then to register a user before they can see the details of the purchase.
Right now first they can see a confuse page when they can register, then there are two option: to put the shipping and billing address. Next the detail of the purchase, then they can choose the shipment method and lastly they can proceed with the purchase. If they are no register in the next page appear the form to register. (Everything in one page)
For me is so confusing, should be like amazon, when the custumer proceed to the purchase the first page force then to do loggin, if they alredy have a user or to do the registration.
Please can you help me? I already check the virtuemart options.

I’m afraid that modifications such as this require extensive changes to the theme’s code; I do apologize but such large changes are custom work that are beyond the scope of our technical support.