I have asked my web hosting to install magento 2.1 on my site.
I purchased a theme.
I am following the manual where it says I must upload the app, lib and pub folder to my magento root. The manual does not say i must replace existing files but I did.
But when I start my site, I get
is currently unable to handle this request.
HTTP ERROR 500.
Have a look in /var/logs/ exception.log, debug.log and system.log
These should give you more information on the error you are receiving.