Click here to navigate to IB's main page. Log into the "Account Management" portal with your IB username and password.
On the left menu, click "Account Settings".
On the right hand side, look for the configuration panel, and click the icon to configure your account type.
Change "Account Type" to "Margin". Select "Yes" to change trading permissions.
Click "Continue" and complete the remaining steps.
Please refer to the attached PDF guide for more detailed instructions.