If you received the theme in a ZIP file with the theme, then you can update it manually. In such case, to update theme you will need to use a plugin such as http://wordpress.org/extend/plugins/easy-theme-and-plugin-upgrades/.
This plugin will save a backup of your current theme, delete current theme directory, and replace it with a new version.
If you want to update the theme with below method you will need this plugin installed and activated. Otherwise, the update will fail with an error “The destination directory already exists.”
Will I lose my data when updating theme manually?
You will not lose your data while updating the theme manually or automatically. Nothing is stored in the theme directory, so unless you made changes in theme files you are totally safe.
However, If you made changes in theme files then you should move them to Child theme instead to be safe.
Updating using “Easy Theme and Plugin Upgrades” plugin:
- Log into your WordPress site.
- Go to Appearance → Themes.
- Click the “Add New” button.
- Click the “Upload Theme” button.
- Select the zip file with the new theme version to install.
- Click “Install Now”.