Pro-Sites Registration Page confusion

Really confused how to customize my site so that when new users sign up they either have the option to upgrade to pro sites or use the free option. I have read through the forums here and I'm just lost. I tried using the "no email verification" plugin to solve this but it didn't seem to change anything except the speed of my site. All the threads are old, so please if anyone has found a workaround or explanation of a smooth system (I'm willing to change my business model slightly if need be) let me know. Thanks!