Contact the dealer with whom you want to start using to find out how long it will take to install one of their tanks or one you have purchased.
Monitor the gauge on the LP tank outside your home to see when the contents drop below 15 percent. You might as well use the gas you've already paid for before switching dealers.
Contact your present dealer once the gas level gets to 15 percent so you can schedule the company to remove its tank from your property before it drops below 10 percent.
Call the new dealer once the appointment is set to confirm their arrival to install the tank so you aren't out of fuel for a significant length of time.