ok... this should take you where you need to be if you copy and paste it into your address bar. http://www.mibba.com/users/profile/css/
once you get to this page, scroll down until you see a blue link. it should say something like... Layouts: Click here to use one of our pre-made layouts.
the 'click here' should be the ink and then it's pretty easy from there.
go to your my mibba page and under the heading of 'profile' click on avatar and upload the image of your choice.
I you want I can also tell you where to find layouts that are pre-made and stuff