[header] How to change a keg [title] Check to make sure your keg is empty. [step] You'll know that your keg is empty if you open the faucet of the tap and either very frothy beer comes out or none does. [title] Look to see if your keg has a co2 line. 
[step] Some kegs will have a co2 tank that provides pressure inside the keg to help dispense beer. The gas also helps the beer hold its natural carbonation.