This question has been asked time and time again here in the forums.
Here is a link of one of them (although it explains how to change gameboot, it's the same procedure to change coldboot):
You'll have to use WebMAN MOD in order to enable write access to dev_flash.
Another way is to use multimanMC in order to enable write access to dev_flash and then copy the files the coldboot files.
Here is a video tutorial: