How can I properly care for my old beta fish to ensure its health and well-being?

To properly care for your old betta fish, ensure it has a clean and spacious tank with a stable water temperature between 75-80F. Feed it a balanced diet of high-quality betta fish food and avoid overfeeding. Regularly clean the tank and replace a portion of the water to maintain good water quality. Monitor your betta fish for any signs of illness and consult a veterinarian if needed.