Jailbreaking provides advanced functionalities on an iPhone, however not every iOS version is eligible to have easy jailbreaking facility. For the latest versions of iOS, jailbreaking is a very difficult task. One easy way to achieve jailbreak on iOS is to downgrade the iOS version, but unfortunately iOS can’t be downgraded in any official way.
If you download TinyUmbrella you will have the ability to downgrade your iOS version in future. There used to be unofficial ways by saving SHSH Blobs and using them to downgrade iOS to an earlier version. But Apple has shut down all the loopholes in their iOS system, now SHSH Blobs can’t be saved so downgrading from iOS 9 to iOS 8 or earlier is no longer possible.