iOS 11 Beta 4 is Apple’s first new release in two weeks. iOS 11.3 is expected to bring new battery health features, along with new Animoji and ARKit improvements. You can upgrade to iOS 11.3 Beta 4 using 3uTools now.
It is necessary form the habbit to regularly backup your device just in case.
Process
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 11.3beta4 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 11.3 beta 4 and reboot once or twice during the process.