Why can't I change my YouTube channel art?

On YouTube, I am trying to create a new channel. When I created it, it gave me a channel with my real Google plus name (Lets pretend it was KL23). I didn't want that. So I went under YouTube settings, changed my YouTube username, and it created a SECOND channel (Lets pretend it was FJ49). So now I have both accounts. KL23 and FJ49. I tried different channel art for my account FJ49, until I found the one I wanted. I found a certain picture, and now I'm trying to change it. But the option isn't coming up! It's not letting me change my channel art at all! I am so frustrated! Please help!