It's a whole process using GIMP.
Libertyernie made a tutorial that I copied into Notepad.
Here's a tutorial. It's pretty bare-bones, but if you're good with GIMP hopefully you can figure some of this out. It's much easier for me to do it than to explain it. I might update this later by editing the post.
NOTE: You might want to turn off anti-aliasing in Fuzzy Select and Select by Color tools.
In Image>Canvas Size, increase the image size to about 125% in each direction, then press “Center” before pressing OK. This is to make room for the white glow around the logo later.
Right-click the layer and press “Layer to Image Size.”
Using the Fuzzy Select tool, fill in the empty area on the borders with white.
Select the background (white) areas of the image with the Fuzzy Select tool. You can hold Shift to add to the selection.
Make a new layer. Move it behind the layer with the logo on it. Color the selection in black (the logo should be in front.)
Go to Select>None. Go back to the logo layer.
Go to Select>Grow and grow the selection by 1 pixel.
Go to Colors>Color to Alpha and change all white in the selction to transparent (which is the default.) You should now be able to see the black.
Use Colors>Desaturate to make the logo black & white.
Use Color to Alpha on the logo layer – but use black as the color to be made transparent.
Go back to the black layer and use Fuzzy Select (or Select by Color) to select the black area. Go to Select>Invert.
Grow the selection by a reasonable amount of pixels (this will be the white outline of the logo.) A good guess for the amount is about the width of the original image you started with, divided by 45.
Go to Select>Feather and feather the selection, (about) the same amount you grew the selection by.
Hold Ctrl while using Fuzzy Select (you should still be on the black layer) to remove the logo area from the selection.
Make a new layer. Press Ctrl+. (period key) to fill the selection with white on that layer. If it doesn't look right (too big/small or too much/not enough blurriness), undo a couple steps and try again with different grow/feather values.
Put white layer behind logo, change mode to "Screen"
Use Image>Autocrop Image.
Go to Image>Merge Visible Layers, then Image>Scale Image. Make the image a width of 120 or a height of 56, but don't make it bigger than 120x56 overall.
Change Image>Canvas Size so the image is 120x56.
Right-click the black layer and press “Layer to Image Size.”
Using the Fuzzy Select tool, fill in the empty area on the borders with black.
Bold indicates what I added to my notes.
