all you need is this program i forget what its called but its possible pm ill find out

Just use a usb and mod your gamerscore to 0

I don't think you can legitimately reset/removed your earned Gamerscore. You can delete your game history but that it, to my knowledge atleast.

But if you're determined to reset your Gamerscore, you're going to have to edit it yourself in a modding tool program, you can either use Horizon or another major program, but I'm not sure if you can reset the Gamerscore. Though you can mod your Gamerscore and hope Micrsoft reset's your Gamerscore for modding it(they reseted mine's).