Goodman dual unit

Is changing the balancing point something easy to do? I rent a home that had a new Goodman Dual unit put in feb 2012. I filled up a 100 gallon tank then. That lasted until December 16th 2012. From my understanding that heat pump will be on until it drops below 40 degrees and then the propane will kick on. I checked my gas on MOnday and had 30% checked today and only had 5%. I filled the tank up again on the dec 16th for $320, and called today and it was going to be $480. So basically I have a power bill of $150-$175 and a high gas bill that last a little over a month. I am thinking if I put the balance point to 25-30 that would decrease the gas bill, and it wouldn't cost me as much every month with the power and gas. Also if I run out of gas can I still use the unit just with the electric?