The CO of the squad uploads it via the game where HTC reviews your art. I think its normally included in the next game release. Unless it now gets downloaded to everyone in the background now??
If you cant wait for it, and your CO has given you a copy, then put it in the 'squads' folder (C:\Program Files\HTC\Aces High II\squads by default) of your AH2 installation. It should be named [COs_InGameName].bmp and be 64x64 and 256 colors.