db.changeUserPassword()

changeUserPassword(username, password, mechanism? , digestPassword?)

This method takes two arguments. This method updates a user’s password. 

Note:

Run the method in the database where the user is defined, i.e. the database you created the user.

Example 1: When user not present.

db.changeUserPassword('hello','hello')

uncaught exception: Error: Updating user failed: User hello@users not found :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
DB.prototype.updateUser@src/mongo/shell/db.js:1417:11
DB.prototype.changeUserPassword@src/mongo/shell/db.js:1421:5
@(shell):1:1

Example 2: When user is present.

db.changeUserPassword('userName','newPassword')