You can up- or downgrade your membership easily in your account settings. Here's how it's done:
- Log in to your Subba-profile
- Head over to My Account
- Click the 'up- or downgrade' button
- Select the membership you would like
You will switch automatically to the new membership on the end-date of your current membership.
Heads up: Up- or downgrading is not possible when your payment is being processed.