Simple update

Connect on your mongoDB, then connect in your dabatase.

"mymongo":PRIMARY> show dbs;
admin         0.203GB
foo_db        0.078GB
test          (empty)
use foo_db;

Display your collections

"mymongo":PRIMARY> show collections;
settings
system.indexes
users

In my case I want to search a user named user1

db.foo.find({"username":"user1"} )
{ "_id" : ObjectId("55d09bfd9f9c7e617300001b"), "username" : "user1"}

Now I want to change the username user1 to updatedUser1

db.foo.update({ "username" : "user1"},
    { $set:
      { "username" : "updatedUser1"}
    })

Nasted update

For nasted entries you will first search normally for the user you want:

db.foo.find({"username":"nasted_user1"} )

The return will be something like below, here you can see that inside address you have zipcode.

{
  "username" : "nasted_user1",
  "addresses" : [
    {
      "zipcode" : "01156040"
    }
  ],
}

To access the entry above and change you need to use . like the example below with the user nasted_user1 where is changed his zicode.

db.foo.update({ "username" : "nasted_user1"},
  { $set:
    { "addresses.zipcode": "12341234"}
  })