The beta is currently available only for those who sign up for the developer program, but the public beta will soon follow.
Follow these steps to get the iOS 9 beta on your device now.
Make a Device backup
Beta version of the software may have bugs and so it is safe to create a backup of your personal data before your proceed. Connect your device to iTunes or iCloud and perform the backup.
Make sure all your purchases are also backed up into iTunes.
Be a part of Developer Program
Once you register for the developer program, you will get to download the iOS 9 Beta for your device. You will also get a number of other uses such as support for app development and so on.
Download the Pre-release of iOS 9
Once you sign up as the developer, you will be able to download the beta from the downloads section of their website. Select your device and model and get the appropriate file.
Register your device for Apple Developer Program
Apple makes it mandatory for you to register your device in which the beta is being installed. Only then the update would be smooth else there are chances that you get your phone bricked.
Go to the Accounts section and in Devices, add your device in which the beta is going to be installed. It would then ask for the UDID of your device which can be found in tour iTunes itself.
Now, your are all set to update your device for a new experience. Connect your device to iTunes. Extract the file that was downloaded earlier. Hols down “Shift” button on keyboard and click on “Check for updates” or “Restore Phone”. Use “Options” button when you are using a Mac.
You will get to select the source of update. Choose the file in the extracted folder and click on open. iTunes will check for your update and ask for confirmation. Once its approves, you will be on iOS 9 in no time.
The update comes with features such as predictive search, multitasking environment for the iPad, transit information in Maps and lot more.