What do I need to do to recalibrate my printer after updating the firmware?
If it is Marlin based or RepRap based, many parameters are stored in EEPROM memory. A G-code command M502: Read parameters from "configuration.h" would reset all parameters that can be changed to their default value as defined in your configuration file. Don't forget to follow the M502 command with a M500 command to store the loaded parameters to EEPROM. This would overwrite all previous settings.

From the linked source, M502:


  This command resets all tunable parameters to their default values, as set in the firmware. This doesn't reset any parameters stored in the EEPROM, so it must be followed with M500 if you want to do that.


You can send these commands over a terminal interface to the printer using applications such as Pronterface, OctoPrint, Repetier-Host, and probably many more, or store the commands in a G-code file (e.g. a text file with a .g extension) and print the file using an SD card.