There are no separate installation files of AJAX Register for different Joomla versions. Everything is contained within a single installation file package. Just upload it to Joomla installer and the right component will be installed depending on your Joomla version.
The upgrade is free for existing AJAX Register customers within the subscription period.
For more information visit the AJAX Register product page. See it in action on DEMO site.
Get it now here: purchase AJAX Register.
As a sidenote, AJAX Scroller is also compatible with recently released Joomla 1.7.