Ahead of the official launch on September 19th, Apple, at its Steve Jobs Theater event, rolled out the master build of iOS 11 to developers and public beta testers. This version of iOS 11 should be very close to finished.
Once you sign-up for the program, you just have to open the beta website with Safari on your iPhone or iPad and follow the directions. A profile will be downloaded to your iOS device. Just restart it, and then head to the update menu. Make sure to back up your device before the upgrade. Apple has given instructions on how to do that here.
After the iOS 11 is downloaded onto your device, you can start the install process. And after the installation process is completed, you can enjoy the latest version of Apple’s mobile OS and the new features that come with the update, including an overhauled Control Center, peer-to-peer Apple Pay payments, much more powerful iPad multitasking, and many more.