From setup page navigate to Build -> Customize -> Contacts -> Page Layouts.
By clicking on the ‘Page Layouts’ link, you will be redirected to the Contact Page Layout page.
Now click on the ‘Edit’ button beside ‘Contact Layout’ to edit that layout.
On clicking the ‘Edit’ button, you will be redirected to the Edit View of the Contact Layout.
Now drag the ‘Username, Password, Customer Portal Role and Enable Portal Checkbox’ field to the Contact Detail section and click on the ‘Save’ button to save the changes.