Don't like the default picture that shows up beside your posts? You can delete it or change it to whatever you like. To do so,

1. click on "my account" under the navigation block (the block with your user name on it).
2. click on the "edit" tab at the top of your profile.
3. scroll down to the picture settings. If you want to delete the picture, click on "delete". If you want to change the picture to something that represents you, then click on "upload" and then choose the picture you want from your files.
4. click on "submit" at the end of the page.