Choose your account, and select Channel Details under the Manage your Channel dropdown box, here you can update your business details, company logo, billing information and upgrade your account.
Enter the relevant information and hit 'Save'.
To add/update your Billing info, select the 'Billing information' tab.
To upgrade your account subscription, underneath the Billing icon select the 'Upgrade' icon.
This gives you the option to change your account subscription if your needs are not being met.