If you wish to have a safe wordpress themes, install it from your dashboard. This is what my web hosting provider suggested last week. Most of the themes from free sites have invisible codes which are prone to hacking , not SEo friendly and can consume bigger space. Yes is true that their designs are nice and trendy but they are just bait. I experienced it last year when my health blog was hacked. My web host provider fixed it by changing the theme.
WordPress has a lot of new themes which are simple yet elegant like the theme on this blog. So why upload from free sites when you can have lots of safe themes to choose from your dashboard?