If the plan you purchased costs less than the plan you wanted, you can "upgrade" yourself to the correct plan via your account page without it costing you anything.
If you need to switch from a monthly or annual Minecraft to Roblox account (or vice versa) you can follow this process:
On your billing account, select the plan tab to view your current plan. Select the "Change plan" button.
You'll automatically be shown your upgrade options. However, you should select the tab for which account type (Minecraft or Roblox) you want to switch to.
Select the monthly plan option. Then simply checkout by clicking the green pay button. Do note, when you switch a subscription, your plan won't charge you until the next payment date!
If you have a lifetime plan you need to switch, please contact customer support.
If you want to upgrade to a family account, you can do so via the plan tab on your account page found at codekingdoms.com/account/. You can't downgrade a monthly family plan to individual. If you want to do this, you are best to cancel that subscription and sign up again. Let customer support know so they can refund your original account.
If the plan you purchased costs more than the plan you wanted, let us know and we can arrange a partial refund and downgrade your account manually.