How to adjust peaks and valleys via noise?

Hello all. 
I'm looking to adjust how my hills and valleys look via noise - specifically, I'd like to make them shorter so a dimension I'm working on can be overall more flat. What I am a bit confused on is which aspect would affect that most. I've tried adjusting the ""ridges" value with custom density settings, which also contains custom noise. 
Is there a different setting I should be adjusting, like erosion, or am I going about things the wrong way?