Considering my previous experience here 559 kb isn't too big, since the image before the one I'm using now was 510 kb. It may be, too, that the 500x500 px thing is perhaps a lil' too much (although larger images are automatically reduced to that size iirc), so an option could be, for example, to try with 460x460 px.
Or using a .jpg format instead of a .png. That works most of the time.

But what's bugging is that Ancie doesn't let me erase the current avatar. xd