As a leader, I will say that there is no point in demanding a promotion.
If we are talking about a promotion, it is worth proposing to the manager your candidacy, saying that the position is interesting, you are ready to take on these responsibilities, you feel your strength and capabilities. As a rule, any manager in the presence of a vacancy with a promotion considers candidates for growth "from the inside", but it never hurts to show that you are interested in growth. In this case, require in no case. You can only demand what you are obliged to give - pay on time, for example, everything else needs to be earned.
If the requirements are justified and you can find another job, then of course it is.
How else will the employer know that you want to get more?
It's true if someone else can do your job. then another, then maybe you should not demand, but talk.