Make sure you have the standalone Git installed. Reboot after installation.
In Unity, open "Window" -> "Package Manager".
Click the "+" sign at the top left corner -> "Add package from git URL..."
Paste this: https://github.com/forcepusher/com.bananaparty.webutility.git#4.0.0
See the minimum required Unity version in the package.json file.
Find "Samples" in the package window and click the "Import" button.
To update the package, simply add it again using a different version tag.
Also see the Development Repo if you want to modify this package.