Apple seeded the first beta of an upcoming iOS 11.4 update to developers and public users, a little under a week after releasing iOS 11.3, an update that introduced a wide range of new features like Battery Health for monitoring the status of your iPhone's battery, Business Chat in Messages, ARKit 1.5 with augmented reality improvements, new Animoji on iPhone X, Health Records from participating medical providers, and more. Check what's new in iOS 11.4 Beta1 here.
It is necessary form the habbit to regularly backup your device just in case.
Step 1 Connect your iDevice to PC with USB cable and then launch 3uTools.
Step 2 After 3uTools successfully connects your iDevice, navigate to "Flash & JB" -> "Easy Flash", there are compatible iOS versions options and please select iOS 11.4 beta1 firmware. (Select the checkbox "Retain User's Data While Flashing" if you want to reserve data on your device.)
After you click "Flash", there will be a popup, read it deliberately and click "OK" to start flashing.
Step 3 Please do not disconnect your iDevice until the update has finished. It can take a few minutes. Your device will be updated to iOS 11.4 beta1 and reboot once or twice during the process.