I have to replace my Whirlpool Flame Lock water heater. I am having a little problem removing the natural gas feed to the tank. Can anyone tell me which way to turn the union to unscrew the attachment?

I need to know:
1. should I use the large wrench on the union to hold the pipe steady or am I turning it (clockwise / counter-clockwise)?
2. alternatively, am I turning to small wrench on the bottom of the union and turning there (clockwise / counter-clockwise)?

See picture

Thanks for you help in advance.