my mars wouldn't be recognized in computer

I am trying to upgrade android os 6.0 to 8.1, but my machine wouldn't be
recognized while pressing reset button and inserting usb cable..

my mars display the "No command" when I pressing the reset key while inserting usb. then went into "Recovery Mode" always.. :angry:

I changed usb cable .. and attempt to do it in another computer , but it still doesn't work .

is it problem with my mars? or another things to do recognize the device in computer? :help: