Jack the side of the mower up, rim in the air. Tire tools are very helpful. Soapy water in a spray bottle too. If you remove the rim, you still have to hold the rim to battle the tire/tube off. Leave it on if you can. Some mower tires are a struggle to use a clean word. Or pull the rim and take to a tire shop. Won't cost much. I sleep better when the pros put the tube in.