stripped oil drain plug

was doing/attempting an oil change for a friend on a 3.5 and the bolt was in so tight it rounded the head of the bolt so i bought a new one for when i got this one off but after trying vise grips and only continuing to screw things up i thought it better to stop and ask for suggestions thanks

Are you turning it the correct way?

Yeah what Bleed said.

Also, since the corners are rounded off, take a file and make the bolt square; you should be able to file it so it has two parallel sides that you can put a wrench onto.

lefty loosy righty tighty.