Editing Artwork not created in Illustrator
I have a question about editing artwork that was not created in Illustrator. I have quite a few designs that I have created over the years in a different program. So now I want to start using Illustrator but I can't seem to edit any of the old designs. Just when I think I have it figured out turns out I don't. All I want to do is resize the designs and change the colors. I have the original designs saved as jpg and png files. I followed the first set of instructions here How to import artwork files in Illustrator but I still can't change the color of my design. Does it matter if the original was a jpg or png file? I don't want a white background on the design because they will go on a mockup t-shirt in Photoshop. Can someone point out what I doing wrong here?
