A great little freebie for quick image adjustments is photofiltre.

Then you would just open the picture, right-click and select 'image size' and change it to what you need.

What I get caught by here with avatar files is the file size itself has to be pretty small, so lots of jpg compression is sometimes required. Photofiltre offers the compression ratio as a pop up when using 'save as'.

Very small program, under 2 meg and works quickly with very little resources -
http://photofiltre.en.softonic.com/

I do not work here, but the benefits are still awesome
Make your sound your own!