I'd like to add something to what the others have said here.

First you should see your company as a community, and every community has a culture.

It's going to be extremely hard to change a culture in an existing community. You'll have to identify who the core members are, or opinion leaders, and work with them. This comes with obvious difficulties, for example how will you get them involved in the changes that you wish to apply?

It's easier to start from scratch. I have no experience here and it depends on your exact situation, but you might want to create a new team. The initial people in any community or are going to set the tone and atmosphere and remain influential over time. New members will copy their behavior.

Whichever way you take, you'll want to consider what culture you want. What vision does it have, what values?

Let me make an example here. Say you want developers to be able to say no. It's something a lot of people will be afraid to do, but it can make your company more efficient by avoiding unnecessary work. When you join a new team and you see an existing member doing it, you'll feel safer to do so as well. You might call this value open communication or empowerment.

So you'll want to figure out your exact intent. What vision do you have and what values suit that vision? And what is your strategy to affect company culture?

You have to understand that it isn't going to be a one and done deal, but an ongoing journey.