How to help my team members handle new changes?

This is a tricky one - Growing pains are always tough in a startup. I remember when we introduced levels at Course Hero, and there was a similar reaction. The hard thing about levels in particular is that a bunch of engineers feel like they are incorrectly leveled during the transition.

The thing about levels though is you 100% need them at some point. As a company gets bigger, you need a standardized path for engineers to move up on, and it's better for the engineers as well as they can make their resumes clearer. It's especially helpful for more senior engineers as "Staff Engineer" looks way better than "Software Engineer" on a resume.

I assume your leadership gave you a long list of reasons on why this move was necessary and the benefits it'll bring. I recommend iterating through those with your teammates as much as possible, doing so in an empathetic way. My communication course has some general advice on how to have those tough conversations: Effective Communication For Engineers