From China Stable To China Dev

Apr 1, 2016
hy guys i want to install china dev miui8 on my i have stable china miui7. i need only to download and install it with choose update package or i need to unlock bootloader, i'm asking this because china stable miui8 will come in august so i don't want to wait. if i update with the method above i will lose my data?
P.S. I have also an idea to share with mods, to create a thread in which we explain how to change every rom from any situation so we will help all people with one thread.