You should receive a notice every time the Vendify theme is updated in your email inbox. If you do not please make sure your ThemeForest email address is up to date.
Create a Backup
Important: Take a complete backup of your site before making any changes to your theme: Making a complete backup of your WordPress
Next click on Appearance ▸ Themes ▸ Add New ▸ Upload Theme and select “Choose File”. Choose the
themeforest-9602611-vendify-wordpress-directory-theme-wordpress_theme.zip file which you just downloaded and click on the “Install Now” button then active the newly installed Vendify theme.
Note: If you previously named your theme directory something different than what was originally downloaded you will need to rename the new directory to match. If the directory of the theme changes you will lose your theme-specific customizations such as menu positions and customizer options.