I have 11 betta's and they are all in one gallon containers. I will tell you how I do my water changes, but you will probably discover a method that works best for you. I don't use any substrate in my gallon tanks, but I do keep a small live plant in each tank. Also, I am not sure if you have use a heater on Jojo's tank. If you use a heater, that makes water changes a little more difficult. Some people use heaters in their betta's tanks, but I don't. The house stays warm enough to keep the water about 78 degrees.
I use empty one gallon milk containers to store tap water in until it's time for a water change. With 11 betta's I have to keep a dozen on hand. This allows the water to age a bit and also come to room temperature. You always want to make sure that the clean water is the same temperature as the old water.
Just net Jojo and put him in a small container with a small amount of his old water in it while you are cleaning his tank. You can use white vinegar to clean Jojo's tank if it is made of plastic or if it's made of glass, you can use a little aquarium salt or the vinegar. ( salt would scratch plastic) Just be sure to rinse it well. Then pour in your clean, aged, room temperature water into his bowl. I also add a small amount of "Stress Coat" to remove chlorine and chloramines. "Stress Coat" is just one of many products available for this purpose. It also contains Aloe Vera, which is beneficial to Jojo's slime coating on his skin. Then just net Jojo and put him in his clean tank.
(sometimes bettas get a little nervous and jump, so hold your hand over the net during the transfer)
If Jojo has a heater on his tank, you will need to use a thermometer and make sure the water you put in Jojo's tank is the same temp as the clean water you are adding back by mixing a small amount of warm water until you reach the correct temp. Also, make sure you unplug the heater and let it set about 20 minutes before you plug it back in until it has time to adjust to the clean water or it might crack the heater.
Also, if you use a substrate, you can just rinse it with running water and add it back to Jojo's clean tank before you fill it with the clean water. Depending on the size of Jojo's tank, you will probably have to do a water change a couple times a week. Even though the water looks clean, fish excreet urine constantly and that adds ammonia to their water and that is what is harmful to their health. In a large filtered tank, bacteria grows over a period of time in your substrate that actually "eats" the ammonia the fish excrete, but in a small betta tank, this cycling process does not have the oportunity to occur.
I know I've probably made this water change operation sound like performing brain surgery, but actually it is very easy! lol With 11 one gallon tanks, I have to do a few everday! I hope this helps you and good luck with Jojo. I've had bettas that have lived to be quite old. (Their life span is about two years)