I managed to alter the Pronterface settings by changing the gcode manually ( mm layer height). I downloaded a stl file named bunny- and started printing. Everything started well, but the printer started skipping some steps on the X and Y axis. The LM8UU bearing, bought on Ebay, didn't slide as they should. I printed the same file again, after replacing all X and Y axis with new bearings (gave me a chance to make some pictures of the Y-carriage). Now everything is working like a real 3d printer! The last picture (left) shows the first layers with a honeycomb structure.