If you are keeping your betta in a one or 2-gallon home, then you should be performing a 100% water change at least every week. Many bettakeepers fail when they try to "cycle" a betta in a 2-gallon... it is simply too small and the betta inevitably gets fin rot. Some bettakeepers will perform partial water changes by siphoning (drawing water slowly out via a tube), but this can lead to a build-up of toxic ammonia over time. In any event, you should condition your water with AmQuel® to neutralize any toxic ammonia build-up between water changes. When changing 100% of the water in one and 2-gal containers, one is not attempting to "cycle" these homes and all of the water can be changed and the substrate and plants can be rinsed off without worry about harming the good guy bacteria. Water changes for the 3-gal tanks and up are performed quite differently, though some bettakeepers do change 100% of the water in 3-gals. In these larger tanks, you will have cycled them safely and they will require partial water changes of about 25% every week to every other week with partial gravel vacuuming.
Advocates of siphoning as a means of performing water changes claim that it is less stressful on a betta. There are methods of removing your betta during water changes that are not particularly stressful if done properly. Many bettas can easily be netted, especially if they learn early on that the net is not a "bad" thing. I have bettas, who learned at an early age, that when the net is put in the water, that it is water changing time and they swim into it and are gently pulled out of the water. Extreme patience is the key to properly netting your betta, as they eventually will make a turn and swim into it. If they have been chased around the bowl with a net, you will forever have trouble trying to net them. You can take two nets, placing one behind your betta and the other in front of him. He will turn to avoid the net and end up swimming right into the net that you placed behind him. Another method to easily remove your betta is to lure him to the surface of the water and dip a cup, such as a measuring cup, behind him and he'll go *swoooop* right into the cup along with the water that gets sucked into it. I know of several bettakeepers, who cup their hands in the water, allowing their betta to swim into them and then transfer him this way. If using this method, be cautious that he may decide to take a jump, be careful not to drop your betta and be prepared to be bitten!
When performing a 100% water change, I always sit on the floor because bettas are "jumpers" and have been known to jump and do that perfect swan dive right down the drain of one's sink or take the long fall to the counter or even worse, to the floor! Use the following steps to change the water in one and 2-gallon unheated bowls. This is a very detailed version but changing water is simple, takes very little time to do and with experience, a water change just gets easier and gets done even faster!
1. Dip about one cup of water out of his home and put him in a never-seen-soap container (e.g. new Tupperware bowl with lid). Soaps, cleaning agents and chemicals are very poisonous to bettas, so never use any equipment that has come into contact with these.
2. Note the temperature of his water from the stick-on-the-outside thermometer.
3. Transfer your betta from his home using one of the methods above and place him in his temporary container that now contains some of his "old" water.
4. Place the lid on top of his temporary bowl to prevent him from jumping. Be sure that you leave a good layer of air between the water's surface and the lid, so that he can breathe.
5. Remove the plants and decorations.
6. Empty all the water out of the bowl, while emptying your substrate (marbles, rocks, etc.) into a never-seen-soap strainer.
7. Rinse the bowl both inside and out with very warm water and wipe dry with a paper towel.
8. Rinse your substrate off well in the strainer with very warm water.
9. Plastic or silk plants and decorations can also be rinsed off at this time.
10. Rebuild his home by replacing the substrate, plants, etc.
11. Add tap water back to his home, which is the same temperature as you made note of in #2. Use your stick-on-the-outside thermometer to determine that you have reached the same temperature. You can dedicate a brand new never-seen-soap bucket with water in it and let it sit out for 24 hours before the water change, so that this water will be room temperature, which would be the same temperature as his old water was (providing that you are not using a heater). Still remember to check the temp on the thermometer after pouring in the water from the bucket to be sure that it is the same temperature as his old water was.
12. Condition the water with proper water conditioners for your particular water supply, such as with AmQuel® and NovAqua®. When using AmQuel® and NovAqua® as water conditioners, after shaking the bottles well, add 10 drops of each per gallon of water.
13. You can immediately put your betta back into his home by either using the net, cup or you can gently pour him back in from his temporary container.
14. Put the lid back on and you're set!