How do I upgrade the theme? Will I lose all my changes?
To upgrade the theme:
Download the latest version from envato (installable Wordpress file)
In admin dashboard:
remove the old theme and install the new version
using FTP remove the theme folder from /wp-content/themes/ and then copy the new version
You will not lose the changes if you added content, uploaded media or changed theme/page options.
if you haven't modified the theme files you should be fine.