Can I sell the things I crocheted using a pattern I didn't make?

I was thinking of selling some of the things I crocheted, but I used other people's patterns to make them. Can I sell them since I made them or not? If not, can I change the pattern a little and then sell them? I want to make like a superman and other stuff to sell at a convention, but I don't want to get in trouble for it. Thanks for any help!