Problem with Marlin

Hi everybody,

I'm new in the world of the 3D printing , i've decided to build a Kossel mini.
I sourced most of the parts from builda3Dprinter.eu and downloaded my first firmware from there.
But now i want to use RichCattell's version to have the auto bed leveling but i have a problem.

When i change some variables in the configuration.h file it doesn't work !
when i change the #define DEFAULT_AXIS_STEPS_PER_UNIT or the #define MANUAL_Z_HOME_POS
nothing changes after uploading to my printer.
I know that the uploading is successful because changing some variable like the bed thermistor works
But when i change it into my old Marlin version it is effective so i would like to know why it doesn't change ?

Thank you very much

Canaylan