Editing on Muse Score 4

Hello, I am creating a variety of scores for a musical partner who is a guitarist ( I am a pianist). I am pretty comfortable entering notes and chords at this point. I am still struggling with a few items including :

1) how do delete extra measures and entire lines of music that are no longer needed in the score. I tried using a variety of combinations of the command and delete key but nothing seems to work.

2) my partner needs some of the chord markings to be slightly larger and I am not quite sure how to do that either.
Thanks so much !