If you have a JavaScript / jQuery error on your admin, then the jQuery script that is responsible to close when you click on the Use Free Version button won’t work.
You can simply check it in Chrome Developer Console. Just press Shift + Control + I then switch to the Console tab. If you see any red line, that means any of your plugin or the theme generating a JavaScript / jQuery error on your admin.
The Use Free Version should close it and the blue button redirects to the PRO version page.
Just checked it on my website with WP 4.6.1 and worked well.
Regards,
Pantherius