Making changes directly in the configuration files is very simple, you just open the file with a text editor (there are lots of different ones, available.) Simply use a file browser to open the "linuxcnc" folder in you home dir, then open the folder "configs". Whithin that folder there will be one or more folders containing the configuration files for your machine(s). Open that folder and in there are your .hal and .ini files. If you double click on one of those configuration files the file browser is smart enough to open the file in a text editor. You can then type in the changes you want to make and resave the file. You will find a SCALE = ??? under each [AXIS_n] section in the .ini file, that is where you make your change.
Alternatively, while Linuxcnc is running you can change the scale from the Calibration item in the Machine pull down menu (assuming the Axis gui). Here you can test your new scale setting, and then save your changes once you are happy with them.