well when you go to set your profile picture you have to supply image in png format. The attached one from HNSB is that.
Or if you have the picture in a bigger resolution than in your avatar you can convert it yourself and get a better looking png.
I just typed 'convert to png' on google and there were a ton of online converters who can do from whatever your format to png.

I'm sure it's not that complicated as it seems. After all you were able to set up an avatar.