OK, this is silly. Going to a shop is fine. For those who can't do that just use a 7-8 inch wrench and put as much force as you reasonably can on it by hand (not standing on it - close enough.

If you are concerned about getting at least roughly the right amount of torque here's a diy solution off the top of my head. Do the calculation for what lbs/kgs of pressure is needed for the length of wrench you have (using the center of your hand on the wrench as the distance). Push down on a bathroom scale a few times until you have a sense of how that pressure feels. Loosen the bolt then tighten to that same feel.