Installing a Child Theme
Child theme is the best way to customize your theme. If you made changes inside the parent theme files directly, all the changes will be lost when you update the theme. On the other hand, when you use a child theme and make customizations, the changes will remain even if you update the theme. Installing a child theme is as easy as a regular theme.
Step 1 - Navigate to Appearance > Themes.
Step 2 - Click "Add New Theme", then "Upload Theme".
Step 3 - Click "Choose File", then select hummingbird-child.zip. You can find the file in uploads folder of the whole package downloaded from ThemeForest.
Step 4 - Click "Install Now" and activate the theme after installing it.