Have a vision for what you want to create, and take steps to create it, but don’t expect it to happen as soon as you’re ready for it to happen.
How much you want to change and how much you can change are two different things.
When you enter a new position, or take on a new responsibility, it is almost never starting something from scratch. You are shouldering the history, traditions, habits, and quirks of how things have been done up to the day you take over. Very occasionally, you get to start something with no expectations. But even then, we settle into ruts and patterns almost immediately, and within a cycle or two, you are stuck into those patterns.
If you want to change things, then, the important thing is to know how much you can change, and how fast you can change it. Learn what’s important, learn how things are done, and then take the smallest viable changes you can, always communicating the why that goes along with the change.
It’s going to take longer than you think to make appreciable change happen. Patience is key.
Along the way, too, you might find that the patterns of the past were adopted for a reason, and as you learn the culture better, you might find you have less motivation to change things at all.
If the change is worth making, then start now and commit to the duration. It can happen, if you really commit. In time.