TD Next is not another program, it's the same, just an update. Please log out of your account from all locations, and back in again. You should already have Next.
how do I move my original todoist lists to the new todoist next?
As Brendon mentioned, Todoist Next is not a new app, it's an update to Todoist. If you log out and back into your account, the account will have Next automatically and you don't have to move any of your data to a new account. Each Todoist account is now Next.
Is there a new screen format on the Mac? I have logged out and back in and I still have the same Premium format. Thanx.
If you have logged out and back in again then you are TD Next. To confirm if you have the latest Mac app, sign into your account at Todoist.com, and if it looks like the Mac app, then it's updated.
You can of course grab the latest Mac App from http://todoist.com/mac