With an Apple developer account, you can install the iOS 13 beta. Warning: you should backup your existing device before installing the iOS 13 beta, and “install only on systems you are prepared to erase if necessary.”
From the Apple Developer Download page, you can find the Restore Images. Find your device among the list at https://developer.apple.com/download/#ios-restore-images-iphone-new to download the .ipsw
Next use iTunes & follow Apple’s guide (Installation Using the Restore Image)
- Make sure you are running the latest version of iTunes on your Mac.
- Open iTunes on your Mac.
- Connect your iOS device to your computer with the cable that came with your device.
- If you’re prompted for your device passcode or to Trust This Computer, follow the onscreen steps. If you forget your passcode, help is available.
- Select your iOS device when it appears in iTunes.
- In the Summary panel, hold the Option key and click the Check for Update button.
- Select the iOS beta software restore image and click Open to start the installation.
- After installing the beta, your device will reboot and will require a network connection to complete activation.
Follow the on screen instructions and you’ll have iOS 13 beta running on your device.
Note: I ran into an error “Can’t install the software because it is not currently available from the Software Update server”. I waited for my iPhone to fully boot up and I’m able to use iOS 13 beta (despite that error message).
Overall, the experience wasn’t too bad. This is a developer beta and not intended for widespread public distribution. If you are interested in the public beta for iOS 13, you can sign up here https://beta.apple.com/sp/betaprogram/