Putting a picture on your profile! Help!

Hello All. I want to put a picture of myself on my profile, as my picture. But, everytime I try to the picture is either too big, too small, or too high! I really need help about this. Please and Thank You! (:

So what size do you use? I've tried many sizes on my computer, but they all still say too big! Haha, and thank you very much(:

Yay! :D I got one!!! Thank you very much(: