Edit time signature - can't seem to do it...

regarding musicscore version 2.2.1 - I can't seem to edit the time signature in the example tutorial. I am transcribing an early 80's piece of fusion music that starts in 17/8 and has a 4/4 section and another 7/8 section, so it is imperative that the software does this, or else I have to find something else to use. It's hard to believe that this is so difficult to find. Everything else was a breeze. Thanks for any help you can provide.