How do you delete some of the effects you don't want in photobooth?

You don’t. I’m not sure why you would want too. They use Core Image to do the effects. Even if you could delete them you wouldn’t save any space by doing so. But you would break so much stuff outside of PhotoBooth.

No i downloaded some, didnt like them and deleted them or so I thaught but they are still there…

Oh… Those should be in /Library/Compositions

I was thinking you wanted to get rid of the default ones.

Do you mean you want to delete effects you have already used on a photo? If that is what you mean go back in history and you can delete a predetermined # of the last things you did. Or you can revert to the original pic.

Is that what you mean?