I'm thinking of changing my behavior.
What do you want to change?
I don't want to be seen as a clown anymore.
It's good to change your behavior if it's seen as foolish by others. Making a positive change in your behavior will help you to move on with your life and feel better.
I need to act more like a douche.
While I think it's a good idea for you to try to be more serious, I have to object to you wanting to be a douche. It is one thing to be too jocular and fun-loving, but to actually try to become inconsiderate of others is not acceptable. Acting like a douche is not something you should aspire to.