on second thoughts

We use this expression to say that we have changed our mind about something.

我们用这个短语来表示我们对某事改变了主意。

At first, she wanted to call the guards, but on second thoughts she changed her mind.

起先，她想叫卫兵，但是一转念又改变了主意。

I know I had agreed to let you go to the cinema, but on second thoughts, you should stay at home and finish your homework.

我知道我曾同意你去看电影，但经过重新考虑，你应该呆在家里完成你的作业。