How to manually change skill level.

You can't change it now. You might have started at 800, which is as low as you can start off with. However, all your ratings are below that already.
Your blitz rating is already below 300 and your bullet and rapid ratings are inithe 600's.

I am an average player but I think my skill level which I chose is incorrect I have defeated players about 50 elos above me and the annoying part is I want to keep on playing to push up my elo rating