If you want leverage in any negotiating situation, you need to be able to walk away from the negotiation if the final terms are undesirable. The party with the best "next-best option" is usually the one most willing to stand their ground on terms, or walk.
That means you need to be prepared to lose your job when you discuss changing its terms, which implies BOTH that you should have other offers AND that you should know your boss might fire you on the spot (or worse, talk you into rejecting the other offers and also quietly stop considering you for advancement in your current role).