Problem Atmel Studio 7 with uploading
...Specify a programmer using the -c option and try again


For Arduino, the programmer switch must be -c arduino. The full arguments for avrdude, in the Atmel Studio 7 External Tools window, are:

-c arduino -p m328p -P COM3 -b 57600 -D -V -U flash:w:"$(TargetDir)$(TargetName).hex":a


See avrdude options.