Skin cpw

Anyone knows a better way to edit the alpha channel for the main-bg.bmp image?
atm i am getting the magenta color with eyedropper tool and then put it where i want it to be trasparent, tought this take a lot of time...(cause the brush leaves a bit of magenta color on the edges)
so i was questioning myself if there is a better way to do this
P.S. tryed by first saving in png with alpha channel and then save to bmp (normal way)but didnt work...

Nvm i found hwo to do it lol
for those that dont know just use the color #ff00ff for background and it will set it as trasparent