You can upgrade and pay for an account with a credit card if you need private repositories for private projects.
In the top right corner of GitHub, click your profile photo, then click Your profile.
On the left side of your profile page, under "Organizations", click the icon for your organization.
Under your organization name, click Settings.
In your organization's Settings sidebar, click Billing.
Under "Plan", click Upgrade.
Under "Plan duration", choose whether you want to be billed monthly or yearly.
Type your credit card information.
Review the information about the charge and your billing date, then click Upgrade to finish upgrading your account.
For more information on how this affects your billing cycle, see "How does upgrading affect the billing process?".