This Is Public Beta MIUI 10 So You Don;t Need To Unlock Bootloader. You Can Easily Update Via Updater App.

Just Download Update Zip File And Go To Updater App Or Settings About Clicl On Three Dots Choose Update Package Select That Zip. Before Update Must Backup Your All Data Becoz This Is Beta So Your All Data Will Be Formated . If Shows Error Please Update Stable Update First Then Try.

This IS Closed Beta MIUI 10 Dowloads So You Need Unlocked Boot Loader.