You'll need to tag your photos before they're uploaded to the website.
You can do this in Windows Explorer (a.k.a. "My Computer" / "Computer").
In Windows Vista, Windows 7, and Windows 8 when you highlight multiple photos, you should get a pane that opens below or to the right of your files that shows metadata and you can just click the 'Author' field there, fill in your name, and press [Enter] to apply the information.
In Windows xp, you can highlight your photos, right click one of them, click 'Properties', click the 'Summary' tab, scroll down to find the 'Author' field, type in your name, and then click either [Apply] or [OK] to write your name into the photos' metadata.
You can also see which names are applied to which photos by choosing 'Details' view in Windows Explorer/My Computer, right clicking on the category bar at the top, right clicking it, clicking 'More', and then check the checkbox for 'Authors'.