With Repetier Host:
Connect to your printer and go to Config → Firmware EEPROM Configuration and edit the E-steps setting. Make sure to save afterwards.
Over USB Connection without Repetier Host:
Use a printer control software to connect to your printer. Send the command M92 E<your number here>to your printer. Then, send M500 to store your settings
In the Online Configuration tool:
In the Tools tab, scroll down to Extruder and update the Resolution number. If you have EEPROM, go to the General tab and switch the EEPROM usage to a different EEPROM Set to overwrite your printer's settings.
If you don't have EEPROM, or want your firmware to be consistant with your EEPROM:
Update the following line with your new value: #define EXT0_STEPS_PER_MM <your number here>. Upload your firmware as normal.
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