I bought my xiaomi mi max 2 weeks back which came with bloatware that caused popups everytime i opened the hp to use. So I reset and left it i one corner until I had the time to flash a new rom since the updater app didn't allow to update to official rom.
Step 1: Apply here to unlock device. Needed to use Fastboot method. Mine got approved in few days. Reason I used was 'I want to update to global rom'.
http://en.miui.com/unlock/
Step 2: Download FASTBOOT Rom.
http://en.miui.com/thread-291059-1-1.html
Step 3: Download and install miflash tool. Guide has the link to download and guide to install.
http://xiaomitips.com/download/miui-rom-flashing-tool/
Step 4: Use the guide in this link to flash to official rom. I followed exactly and did the flashing successfully. Take note you need to use WINrar to unzip the downloaded rom. Link below if you do not have the app.
http://xiaomitips.com/guide/fastboot-bootloop-hardbrick-softbrick/
http://download.cnet.com/WinRAR-64-bit/3000-2250_4-10965579.html
Lastly, this guide will install google apps. You will need a miui account and one reply to get the link.
http://en.miui.com/thread-286862-1-1.html
The steps above will work if you follow the information correctly. Fyi, I installed TWRP and wiped out the existing vendor OS and the phone was without an OS until I dug up more info. Still managed to recover so can be done. I read too many guides and mixed up the methods when it should have been quite straight forward. Good Luck.