like @mastory said it's compiled into a .hex file, and it's not possible to edit those values if you only have the .hex file, you'll need to compile it yourself.
Assuming you have a UM2 it is here: https://github.com/Ultimaker/Ultimaker2Marlin/blob/master/Marlin/Configuration.h
Download marlin from github (then edit the confguration.h to fit) and use the arduino IDE to compile on windows (or just type make if you're on Linux) then use cura to upload your custom firmware.
or have a look here: https://ultimaker.com/en/community/38154-how-to-build-marlin-the-way-tinkerghome-and-ultimaker-do-it-if-you-have-windows
You may not have one on your system. It would only be there if you have previously either downloaded and/or configured it for upload to your printer. Configuration.h gets compiled in Arduino and the result is uploaded into your printer. If you've never messed with it, it probably doesn't exist on your PC. I'm no expert. If you wish to make changes, you'll need to research the best firmware for your needs, download the package and make your configuration.h edits starting there.
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