Apple has released the second iOS 10.3.3 beta for iPhone, iPad, and iPod touch. The first beta version only included new wallpapers for the 12.9-inch iPad Pro and no other visible changes. iOS 10.3.3 beta 2 is currently available to registered developers; a public beta version for iOS 10.3.3 is also available in 3uTools.

Step1: Download and install the latest 3uTools on your PC. Before upgrading, you'd better backup your iDevice. Connect your iPhone to PC with an USB cable. Then head to "Flash & Jailbreak” section in 3uTools, click "Easy flash". 

Note: If you want to retain the data, please select the option " Retain User's Data While Flashing".

Step2: Select or download the latest iOS 10.3.3beta2 on this page, and then click "Flash" button. 

Step3: Keep a good connection between iDevice and PC, and then just wait until this process is finished.