Is there a way to change the time signature and the note durations in a finished song?

I finished notating a song and realized it would make better sense if all the 8th notes were quarter notes, quarter notes were half notes, etc. So all the measures would have to be split in half. I can split measures one at a time but can't fix the note durations. I want to be able to select the whole song and tell it to double all the note durations and change the bar lines accordingly.