gen 6 electronics cant update my firmware

Hi every 1 need some help I'm tying to update the firmware on reprap prusa with gen 6 electronics running marlin. I have upgraded some parts and need to alter my firmware but in the arduino ide I have tried every board and it fails to upload every time some times it wont even compile. I get all sorts of fail messages like .....................................................

(avrdude: stk500_getsync(): not in sync: resp=0x9c)

(avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer)

please please please can some1 help me...