These new versions were announced earlier this month at Developer conferences and we found many viral previews of Developer versions. Apple now decided based on stable testing to release the bets versions for the general public who enrolls for the beta program.
You can sign up on the Beta Apple Website and Once registered you will get all the updates till the final release of these versions. Apple is anticipating to Launch the finalized version by fall.
The Beta Version was expected to be launch in July, But due to stable response, Apple launched it one week earlier. Regardless, As a beta version, you can expect bugs, performance issues, and compatibility with few apps.
Keeping that in mind It may not be a great idea to install them on your primary device(s).