Updating your theme to the latest version is same as installing it. However, it's always a good idea to backup your database for safety. When you update the theme, all direct changes made inside the parent theme files will be overwritten. It's strongly recommended that making changes in a child theme. Also if you translated your theme, copy .po and .mo files to a safe place and copy them back after installing a new update.
Step 1 - Navigate to Appearance > Themes.
Step 2 - Activate a different theme such as Twenty Seventeen.
Step 3 - Hover over Hummingbird and click "Theme Details".
Step 4 - Click "Delete" on the bottom right corner, then "OK".
Step 5 - The rest is same as installing a new theme. Click here to read the section.