How to replace picture in picasa???

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well, i upload a picture a few weeks back. I sent the url of that pix to my friend say http://lh4.ggpht.com/_0yM5hUgVseI/SefIs_g5xbI/AAAAAAAAAE4/ElB94CaWZus/Silvester.gif Now, I've changed my mind and i want to replace that pic with some other pic with the same url. Ya, i want to delete the old file and put another picture and get the same url... please help me i do that i picasa web album??? I really need to know this as soon as possible. Please help me if you know how to do it. Thank you a lot.....