How do you update schema changes in MongoDB

As we all know that database schemas is open to updates and changes as app becomes more large, i cant really find any help on updating schemas for my application. Coming from Relational database background, Its easy to add column to an existing table, but as for mongodb, i really cant figure out what to do.

Lets say in a case where a collection has the following schema

    accounts: {
        name: John Doe,
        active: 0,
        suspended: 0
        }

then i already have over 3000 exsiting and active accounts. But i need to know the defaulted ones and add split name to firstname, lastname. This is what the new schema will look like

        accounts: {
        firstname: John,
        lastname: Doe,
        email: someone@email.com,
        active: 0,
        suspended: 0,
        defaulted: 0
        }

How do i go about this changes for all users ?