You have a few options here. One of the options assumes the image is already uploaded on some website. If this is the case, type the image's location to the Enter a URL to an online avatar image
Another one is to use an existing avatar gallery...
If the image hasn't been uploaded yet, you can upload your avatar. To upload, click on the Browse... button beside Upload a new image from your computer and then locate the image on your hard drive. (I don't think you need to access that floppy drive...)
Click on the Update Avatar or Use Selected Avatar button. Before hitting this button, please fasten youe seatbelts because it's going to be a bumpy ride...
To remove your avatar, click on the--surprise, surprise--Remove Avatar button. What, you already knew that? Where are your sources of information coming from?