Ummm. Hi?
I understand you're knew, so I'll go real easy on you. This is in the wrong place. I'll get I guide to move this to the correct location. Try to put it in the right area, next time. Okay?
And to answer your question:
You click on your username listed at the right corner at the top of the site.
Then, you come to your profile. On the left side, there should be 3 options. Edit my Signature, Avatar options, and Edit my Profile. Click the one that says "Avatar Options."
Then you have the option of uploading your own picture, or using one from the TamaTalk gallery. Choose the one you want:
When uploading your own picture, you click the "browse" button, and select the pic you want. After that, click the "Update Avatar" button.
When using one of the tamatalk pictures, You choose the gallery you want, and select the pic you want. Then click "Use selected avatar" at the bottom of the selections
Hope I helped!