Best answer by Mathis
Thanks for posting. I've looked into this. Your current profile picture doesn't seem to be square, it is 2489 × 1400 px. This is the image iTunes picks up to show on the iTunes store. Thus, please upload a version that is somewhere between 1400x1400 and 3000x3000 px.
This should already do the trick. However, I also noticed that you're currently over quota. This means you won't be able to upload more tracks to your account, unless you delete old content, or upgrade to a subscription plan.
Either way, let us know if you have further questions - happy to help.
P.S.: Here are two great resources for podcasting on SoundCloud and for submitting your feed to iTunes: