http://forum.xda-developers.com/showthread.php?t=3034811
http://dl-xda.xposed.info/framework/sdk23/arm64/xposed-v86-sdk23-arm64.zip
Copy unninstaler to phone, just in case.
You dont need root for changing versions. But you need to unlock it first. Search "miui unlock" in google, first link its what you need to do first. Anyway, if you a not a geek guy, dont buy phone with chinese version if you need global.
U a not alone, my phone is not charging from PC. Even with USB3. Is annoying, i was used to charge mobile to PC or laptop, but it seems to RM3 not working.