How to update the theme?
There are 3 ways:
1- If you did not change or edit any of theme files, you can replace all new files instead of old files via FTP (or File Manager of your Control Panel)
2- You can find the changelog of theme and find which files updated in new version and only replace them in your theme instead of old files.
3- Auto update by "Envato Market" plugin, if you want to update your theme always with an easy way you can install "Envato Market" Plugin and use it easily for update the theme.
Download Envato Market Plugin from here: https://github.com/envato/wp-envato-market