Package Negotiation

Hi Everyone, just wondering if anyone has any tips on negotiating a package for a new job. I have just recently been accepted into a role which is moving to a managerial position. I will be working alongside with 10 other team members in the team and I feel this is a bigger role than what I currently am doing as an individual contributor.

The package they offered me is lower than expected and I have done my research and based on what I have found, I odd to be earning xxx but they offered 20% lower than what I have requested.

What is the most amicable and respectful way to renegotiate my package so as to better align with what my actual target is?