改善 (gǎi shàn) means 'to improve' by making a situation, condition, or quality better — it focuses on the result of improvement. 改进 (gǎi jìn) is more about improving by making specific changes or refinements to a method, system, or product. 提高 (tí gāo) means 'to raise' a level, amount, or standard, often used with numbers or abstract levels.