Root functionality allows you to do access hidden folders, change permissions of certain folders that you cannot do without root and run applications that require Super User (Super SU) access. Fortunately rooting HTC Desire 616 is fairly easy. All you have to do is download Kingroot’s apk from here and put it in your device.
Then Open the application ,with Internet on and press the Green Circle and wait for few minutes. That is it, your phone is rooted when you see this screen. close the application and enjoy your rooted HTC Desire 616. Then download Supersu from the play store. Go Supersu settings > click on "Install SuperSu into /system" and then remove Kinguser.
It shall kept in mind that in case something goes wrong, you should be on stock ROM and rooting voids warranty.