I need help with replacing a color...

[Pavkata]

Hello,
Recently I updated my forum's theme and now the main color is white. However my rank icon's background is gray:


Don't ask me why it's a .gif image. I have no idea. I need to change the background to white or transparent. How can I do it? I tried with the pen tool and the selection tool but both turned out quite bad. The shadows weren't right.
Please help! Thanks.

 

[gedstar]

Here you go

With white BG


and transparent PNG