改动 means to make small adjustments or modifications, especially to a text, plan, or arrangement. It's more specific to minor, piecemeal changes than 改变 (which can be a fundamental transformation), and less formal than 更改 (gēnggǎi, used in official contexts). Compared to 修改 (xiūgǎi), 改动 often implies a smaller, more hands-on adjustment.