How to update to MIUI 10 without unlocking the phone bootloader ?

If you are on stable then if you wants to go for beta version. I already tested MIUI 10 beta version it is too buggy. If you wants try beta version then follow below steps.

Here How to update stable rom to beta
Follow these steps

>>Go to settings

>>Then About

>>Then system update

>>Then select choose update package

Then locate your Downloaded Rom file after that your file will verify please note you must have working internet connection.

Note :-)
If you are on stable version of MIUI and updating to beta then your reset completely please create a backup of your device if you don't how to make back-up then please follow this article

How to make back-up of complete phone on MIUI 8-9

Using this steps your phone complete backuped after completion of installing of beta Rom log in using your mi id

Thanks for visit :)