Go to your main page (click on your site logo in the upper left hand corner). Look for the picture of the little blue man to the right of your name: little_man.png. Click on him. You will find yourself at your bio page. The first section is called "Biography." Click on the Edit button on the far right of the page. 

This will generate a pop up window where you can enter your information.

If you have a picture saved on your computer you would like to upload, click on the field to the right of Upload Image and navigate to wherever you have saved your picture. If you want to use a picture stored somewhere else on the internet, enter the URL of that picture in the field next to URL. (Wait, how do I find out what that URL is?

Don't forget to Save! There is a Save button at the bottom left of the pop up box.