Hello

There are in a SVG format, a format based on form instead of pixel, which allow you to change size without any problem. You can open SVG with inkscape. I think Gimp can also open them.

Anyway, if you want them in PNG format, click here :

http://openclipart.org/image/800px/svg_to_png/194632/potionlist.png

You can also go here and choose png size : http://openclipart.org/detail/194632/potions-by-matheod-194632

If you have any trouble, say me :)