Assuming you have eeprom enabled, all you need to do is change values in eeprom.
Also check your ptinter length settings in eeprom.
After changing you might reopen eeprom settings to see if the values got set.
If you have specialproblems with z remember that rods can only move very slow (2-5mm depends on motor, greasing,..) with accelerations of around 50mm/s3. If you try more you get many loosing steps so speed is not what you say.
