Please read about theme update in our documentation -http://www.8theme.com/demo/docs/lifestyle/#theme_installation_and_upgrade
If you edited php files, I would recommend you to transfer changes into a child theme. Your Theme Options settings won’t be lost, but you can export them into file (Theme Options > Import/Export > Options > Import Export > Download data file)
Don’t forget to create a backup of your files and database before starting update process.
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).