Downgrading Your Wix Premium Plan
To downgrade your premium plan, you need to first cancel your plan and unassign it from your site. You can then purchase a more basic plan.
To cancel your current plan: Sign in to your Wix account > hover over Subscriptions > click Premium Plans > next to the relevant plan, click Manage > next to Next Payment, click Cancel payments.
After canceling the payment, return to the Premium Plans page > under the relevant plan, click Unassign.
Now you can upgrade to the plan that you want: From My Sites > next to the relevant site, click Upgrade.
Don't forget to reconnect your domain to your site after canceling and purchasing a new plan.