We typically release a Beta build of a new major version of Zorin OS a few weeks in advance of the full stable release. This Beta version is available for anyone to download for free from our website for testing purposes.
Zorin OS 17 is still under heavy development, so we don't have a Beta build available to test just yet. However, we would recommend you to stay tuned to our Blog over the coming months or subscribe to our newsletter to be the first to know when you'll be able to test a pre-release version of Zorin OS 17.