beaglebone black: i2c1 change frequency


the last week i want to try change the i2c1 (i2c1: 0x4802A000) but i am not very successfull and i dont know why…i have read some sites about device trees and something else but it doesnt work. The biggest problem for me is to understand where i can change something, because some say that you change the am335-boneblack.dtb (/boot/dtbs/3.83…/) and others say that you change in the /libs/firmware and create there an dts.file. So i am a little bit confused.

Can me anybody help?