Apple released the second version of the their developer beta this afternoon, with a slough of enhancements and improvements to iOS 10 previously announced at WWDC three weeks ago. The public beta of iOS 10 is scheduled to be released later this month. However, those with developer accounts who are already testing iOS 10 can download the (OTA) update when connected to Wi-Fi.
As with all developer betas, users are strongly discouraged from loading beta software on their daily driver devices, as they will most likely become unstable and unresponsive at times. Betas are for developers to test their new apps, and from my past experience, this can sometimes make your device unreliable. However, with each new beta release, Apple continues to iterate additional enhancements and updates to iOS while at the same time making it more stable and reliable.