The ".utcfg" file contains configuration for your particular plane, transmitter settings, preferences, etc...
You don't need to get a new ".utcfg" file when you update firmware.
Currently, this file must be generated by uThere support staff for your particular plane, transmitter, and Ruby units. They contain tuning and calibration info as well as your prefrences. If you have lost your ".utcfg" file, contact support@uthere.com.