Before changing the lawn mower battery, make sure that you are wearing all safety gear like Gloves, Glasses. After that, determine where the battery location in the machine and clean the connectors with a mix of water and baking soda to get rid of corrosion, if any. You can use the metal-tipped brush to clean out any corrosion. Start with the negative cable and set it aside and repeat the same with the positive cable. Once the cables and straps are loosened, take out the dead battery. Do not put the dead batter anywhere near to where you are changing the battery. Take help if you need to keep the battery at a faraway place form the workstation. Once the above steps are performed, install the new battery by connecting the positive and negative cable. You could fasten the battery with the help of straps if there were any once the connectors are restarted.