This short tutorial explains the solution to one of the most occuring issues by installing the Pro Version.
Theme Install Failed
The package could not be installed. The theme is missing the style.css stylesheet.
Solution: Install Pro Version as Plugin
Please be aware that the pro version is an add-on plugin, which adds the additional pro features to the base theme.
You therefore have to install the pro version as plugin, not as theme. You can learn how to install plugins in the Install WordPress plugins tutorial.
After you have installed and activated the pro version plugin, you can go to Appearance -> Pro Version and enter your license key in order to get automatic updates.