Instead of starting a new topic every time you have a question about a betta, you can browse through this forum and find all your answers....or you can continue adding to either of the 3 or 4 topics you already started about keeping a betta.
No bother at all. Just thought it would be easier for you to keep track of all the useful knowledge in one topic.
I change 100% of my water once a week on my bare bottom tanks and maybe 25% once a month on my heavily planted vases. If you are going to keep some plants in there, you can do a few 20% water changes a week or one big one once a week.
Being in sunny and warn Los Angeles, I keep my bettas at room temperature. I store a 5g jug of water under the sink and when it's time, I add prime dechlorinator and do a water change.