提高 (tígāo) means 'to raise, increase, or improve' something, focusing on making a level or quality go up (e.g., 提高水平 'raise the standard'). It differs from 增加 (zēngjiā), which is about adding quantity or number (e.g., 增加人数 'increase the number of people'), and from 改进 (gǎijìn) / 改善 (gǎishàn), which mean 'to improve by making changes' — 提高 is about raising the degree, not fixing flaws.