Need some advice here.

Hey everyone, sent me a note and suggested to me that I really should start to improve my artwork and that it doesn't matter if my friends love my artwork the way it is, I should still try to improve it. She kind of said it like this: Are you drawing for fun or do you really see your art as a part of your career?

I asked you that because since I gave you a helpful criticism for you, but you didn't actually do anything. I know your friends love your art, but it wouldn't hurt them if you can take criticism to improve your art. I know, I did this kind of art before but, it still feels better to try to draw in other style than drawing in the same way. I got somewhat to know how to improve to draw characters and other stuff when I was in here and I currently draw them a little bit better now and my friends still liked me when I'm improving it.

Even though I am a bit shocked she would say something like that, I also had a feeling she could be right and I should improve my pics. However, the first thing I should do is start to learn how to shade and I don't think my Untitled paint program is good enough for shading. So I want to ask you all: Do you guys know any advanced art programs I can download for free that will let me make better pics for you all to enjoy? I would really apreciate this if you guys can help me. Thank you for taking the time to read all about this.