Don't know if you're having an issue with the button, you need to be more specific, but to download one of your finished drawings, a little button saying "download" should hover in the lower right corner of your drawing. Click that and it should automatically download to your computer if your browser isn't blocking it.
I haven't changed anything with my computer system and it won't download from the download function on a saved drawing. I have downloaded many of my drawings previously, and since the change, it won't download anything from that button including pictures I have previously downloaded. I can download items from other sites, so it is specifically at this site...