We are a Nintex for Sharepoint 2013 customer and require access to download the new responsive forms. I saw in a few posts that you get access after asking in the forums. I looked for a help link or request access link, but could not find one.
Never used it by myself but you should be able to download your software through the Nintex customer portal
More information can also be found here
Nintex Customer Support Portal Guide - updated ... | Nintex Community
Hope this helps,
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