if you are unaware about how to Flash Xiaomi Stock ROM We are here to help you to solve your problems. You have to follow our step by step guide for upgrade your Xiaomi smartphone in easy way.
Flash Xiaomi Stock ROM Guide
Step 1: First Download Xiaomi USB Drivers and install in your pc. If USB Drivers already installed then SKIP step1.
Step 2: Download Xiaomi Stock ROM firmware zip file and save in PC.
Step 3: Connect your Xiaomi device with pc via USB cable.
Step 4: Transfer firmware zip file from PC to phone SD card (Copy > Paste).
Step 5: Unplug device from PC.
Step 6: From Launcher > Open Tools Folder > Select Updater > Hit Menue key > Select Installation file.
Step 7: Locate Zip file from Your SD card > Click on update button to begin the process.
Step 8: Wait until the process completed and then restart your device.
Before upgrading/downgrading your device you must backup device data.
Source : MIUI