Step 1: Go to this official website of vivo https://www.vivoglobal.com/service.html
Step 2: choose you mobile series.
Step 3:select your phone model
Step 4:go to ‘firmware’ option
Step 5:download the least version zip file
Step 6:after downloading go to the and click on it.It will say confirm to update.just press ok .
Now you have to wait till its get flashed make sure you have 50% of battery left.
Download “poot” app from here : http://googleweblight.com/i?u=http://androidhost.org/get/m382N