how to change difficulty?
That's what ratings are for. If you lose more than you win, your rating goes down and you get matched against weaker opponents until you find someone more or less at your level.
You just joined yesterday, and played only 7 blitz games and 9 rapid games, so your current ratings (437 blitz and 791 rapid) are probably not accurate yet.
Then if you learn something and improve, you will start to win more than you lose and your rating will go up.
I WANT TO CHANGE DIFFICULTY
If you mean the level you chose when creating your account, you can't. Just play games and your rating will quickly get to where it should be.