Thanks for the tips,
I'll give a try.

It is based on 5.1
You should update with clear data ticked.
In order to not lose your apps. you only have to follow these steps:- Go to Settings>Storage& Backup>Data backup & restore>Backup Now. Then update to 6.3G with clear data ticked. After updating, go to backup & restore and you will see the backup you have made. Click on restore and all of your apps (Except Google services and Play Store) will be restored automatically along with their app data. This should save you a lot of time.

why it is not on otg?

5.1

Hello rudra964, just a quick question, Is this based on A 5.1 or 7.0?

I'm currently at 6.2.0.0G, do I need to wipe all while upgrading  

coz I got a lot apps, doesn't wanna setup again.

As flyme 7.0 G might be released in ... emmmm... half a year?  

Upgraded patches to improve system security
Optimized system stability
Optimized system multi-language
Optimized power consumption
Optimized compatibility with third-party apps
Optimized method of saving contacts to improve the user experience
Fixed bug—the default style of home screen icons is not Flyme style after upgraded
Fixed bug—screen flickering in the Camera app
Fixed bug—screenshot shutter sound doesn’t work
Fixed bug—no “Screenshot shutter” switch in “Settings”
Fixed bug—repeated disconnecting and connecting the Car Bluetooth after it was connected
Fixed bug—time displayed on the status bar is not the same with that on the lock screen