Hello @QDH,
Follow the steps below to update theme through FTP:
– Download the zipped package from ThemeForest and extract to your desktop.
– In the extracted package you will find archive Lifestyle_Theme_v.x.x.zip, which is the WordPress theme.
– Extract zip file and upload only extracted lifestyle folder to /wp-content/themes/ folder on your server with overwriting.
If you face any problem, provide us with the screenshot (use such screenshot maker as Lightshot).
Regards