Using York Template, can't install another 7.0 Template?

Site URL: http://www.sashataran.com

Hi,

I am trying to install a new 7.0 Template onto my existing 7.0 site, however it doesn't let me. Whenever I click on "Install New Template" it brings me here (screenshot attached) and then only lets me "Start With" or "Preview" the template. Neither Start with, nor Preview leads me to an option to install the template.

Specifically, I'd like to install Sofia. I've tried selecting "Start With", and it loads for a second before bringing me here (second screenshot of footer).

Is there something I'm missing here?

Thanks for any help!

There are things to know about switching templates in 7.0 they can be very different from each other to the point that things move but not quite in the way you may want or expected: