Remove Blizzard Battle.net Authenticator
There are two ways to can remove your battle.net authenticator. Either you still have the authenticator or you have lost it.
If you still have it log into your battle.net accoutn and go to https://eu.battle.net/account/management/remove-authenticator.html
If you have lost it, typical if you have replaced your old mobile or made a factory reset you have to contact Blizzard to remove it: https://eu.battle.net/account/support/remove-authenticator.html