I will go instead of you.

我替你去。

I found the patient worse instead of better.

我觉得此病人的病情非但没有好转，反而较前加重。

You should be out instead of in on such a fine day.

如此好的天气，你应当外出，不该在室内。

Do not take that chair, take this instead.

不要坐那把椅子，坐这把。