In marlin this can be controlled from the menu if you've got a display. That way you can adjust it without having to upload the firmware for every change. From memory, go to control, motion, z offset.
If you use Pronterface or any program that can send GCODE you can just type into the console when connected: M851 ZX.XX so Z 0.60 will be a 0.60mm offset. This can also be a negative value.
After that store the settings in the EEPROM with M500.
