Change note values and playback annoyance

Hi, I am new to Musescore, so please excuse some basic questions whilst I find my bearings.
1) How do I change note values on a score I am writing. e. change 1/4 note to a 1/8 note value mid score.

2) as I write I check with playback.
I have 32 bars and playback continues to "bounce" through blank measures until the end, which means I have to wait for it to get to the end before I can write more or play back again.
- Is there a simple way to stop the play back as soon as I have heard the section that I wanted to hear?

Thanks....