Several iOS 11 beta 6 testers have reported a string of problems upon installing the latest beta version. Some users have not been able to fully download and install iOS 11 beta 6 as it is hung with the "Preparing Update…" message.
To clear things up, iOS 11 developer beta 6 is similar to iOS 11 public beta 5 with the same build number and features, but they target different pool of testers. If you have been trying to install iOS 11 beta 6 or beta 5 for your Apple device and you were not able to get through the entire process, here's what you can do to solve it:
How to fix iOS 11 beta 6 error
Step 1: If you have been stuck for hours updating your device to iOS 11 beta 6 with the message "Preparing Update" flashed onscreen, you will have to abort the process and head over to Settings. Be sure your device is connected to a Wi-Fi or a stable data connection.
Step 2: Go to General > iPhone Storage. Wait until all data files have been loaded. Take note that this is part of iOS 11 beta to show you information about the storage on the device. Don't be overwhelmed by what you see, take care of that later.
Step 3: Find the iOS over-the-air (OTA) update file and tap it.
Step 4: You have to delete the file to free up some space. This will also allow you to redo the process all over again.
Step 5: Once done, head over to General > Software Update. The iOS 11 beta 6 should be available. Do everything again full circle.
Meanwhile, you can check some of the notable tweaks and improvements that come along with the iOS 11 beta 6 via this link.