You can test the beta version of iOS 10
On Thursday you'll be able to download the public beta of iOS 10. Sign up here.
But I strongly recommend that you don't install the beta unless you're willing to deal with some annoying bugs. This is an early version of the software, and Apple will continue making improvements and fixing bugs until the final version launches this fall along with the next iPhone.
If you have secondary iPhone, or you're willing to risk your everyday device, then go for it.
iMessage has been completely overhauled with new features like third-party apps and larger emojis. Photos can use machine learning to analyze the content of your images and automatically group them into albums. Notifications are easier to manage and you can store customized widgets on a separate page next to your home screen. Siri now works with some third-party apps like Uber and WeChat.
iOS 10 will go through a few more iterations before the final version is ready for everyone. But if you're eager to test all the new features now, give it a shot.