Hi,
Actually I think what it sounds like you want to do is "scale" the time.
You can open your file in Notation Composer and click Staff Symbols -> Time Signature -> Scale notes
ScaleNotes.jpg
You can then change the notation from eg. quarter notes to half notes, and then change the time signature as you wish.
The caveat is that you will want to do this type of operation first as it is effectively a fresh transcription, which will lose any annotations you've added to the score.
ReBar is an excellent tool if the file is in rubato and you need to adjust the barlines in a non-regular or non-linear fashion.
Enjoy!
Sherry