If you amend something that has been written such as a law, or something that is said, you change it in order to improve it or make it more accurate. 修正
verb [vt. 及物动词] 修改，修订；纠正，改正；改善（土壤）的结构（或肥力）；<古>修复；改过自新
The president agreed to amend the constitution and allow multi-party elections. 总统同意了修正宪法并且允许多党选举。
a(离开) + mend(错误) → 离开错误 → 修改， 修订
(amend a bill / rule / law / document 修改法案/规则/法律/文件)