LiveXLive subscriptions cannot be downgraded directly from Premium to Plus.
If you currently have a LiveXLive Premium subscription, and would like to downgrade to LiveXLive Plus, the only way to do this is to cancel your current LiveXLive Premium subscription and wait for your current subscription to end. Once the subscription has run through the remaining portion of your subscription and your account returns to a free Basic account, you can purchase a new LiveXLive Plus subscription.
To cancel your Premium Subscription: Cancel a LiveXLive subscription
To purchase a new Plus Subscription: Purchase a LiveXLive Plus subscription
Note: All custom stations and favorites are saved to your account. Nothing is removed from your account when the subscription ends, so you will not lose any of your music.