How Do I Change The Original Time Signature In Sibelius 6?

When I do so via Create, Time Signature, it leaves the original wrong time signature intact and creates the new one in the bar after or before it. But I want to correct the time signature because I realized that it was wrong after I wrote a bar or so. Do I have to start all over again and create a new file or is there a way to do it by letting my file otherwise intact?

Copy all the notes, click on the first bar and change the time signature, delete any remaining wrong time signatures, then paste all the notes back in. You might not even have to copy and paste notes.

Thanks! I found that I was highlighting the bars before changing. But when I didn't highlight anything, it worked!