If you'd like to upgrade or downgrade your account, you can do so in your account page.

Head to https://app.helloaudio.fm/subscription. This will take you to your current Subscription page. Click "Change Plan" and choose what you'd like to change to.

You'll see the prorated amount due today and what your charges will be in the future.

When you're ready, hit "Continue" to finalize the change.