Suppose you're browsing the internet, and you come to this page:

"That's it!" you say, "that is a photo of my true inner self! I must have it! I must make it my profile pic on AMPSport!" BUT HOW?!

Step 1 is to mouse over the image and right-click.  Then select "Copy Image Location":

Now you can paste (Ctrl-V on Windows, Cmd-V on Mac) the URL of the image wherever you want. You should check to make sure the image looks the way you think it will. Open a new tab, and paste the URL in the address bar of your browser.

Good, test passed.

Now go to your profile, click on the little man icon little_man.png, click on the Edit button to the far right of the Biography section, and paste the URL in the URL field for your AMP Profile picture.

Press Save (in the lower right of the Biography edit dialogue box) and your profile pic will reflect your true self.