You can sharpen an image in GIMP on your computer using the Sharpen tool or the Sharpen filter. Here is a full tutorial on how to do it!

Once installed you need to download BIMP, the Batch Image Manipulation Plugin, and install it (see Wikibooks GIMP/Installing Plugins for the details). Again, easy-peasey.

Make sure to give the extension as “.png”, just specifying the file type as “PNG” does not automatically provide the right extension. And the transparent GlassFish image is available here.