While I do recommend measuring the pressure with a WC, if you want to see if it's the regulator via the lazy way, you can just give the regulator adjustment one full turn clockwise to see if it makes any difference.
The regulator is hung off the propane tanks. There's a cap covering the adjustment screw.
You may note that after adjusting, that your cooktop and all gas appliances may work better immediately with a stronger flame. You'll still want to change out the regulator as it is definitely worn anything over 10 years, and won't provide the propane pressure adequately when more than one device is on.
Regulator adjustment looks something like this (but this is a different tank configuration)