def update_alias(AliasName=None, TargetKeyId=None):
    """
    Updates an alias to map it to a different key.
    An alias is not a property of a key. Therefore, an alias can be mapped to and unmapped from an existing key without changing the properties of the key.
    An alias name can contain only alphanumeric characters, forward slashes (/), underscores (_), and dashes (-). An alias must start with the word "alias" followed by a forward slash (alias/). An alias that begins with "aws" after the forward slash (alias/aws...) is reserved by Amazon Web Services (AWS).
    The alias and the key it is mapped to must be in the same AWS account and the same region.
    See also: AWS API Documentation
    
    Examples
    The following example updates the specified alias to refer to the specified customer master key (CMK).
    Expected Output:
    
    :example: response = client.update_alias(
        AliasName='string',
        TargetKeyId='string'
    )
    
    
    :type AliasName: string
    :param AliasName: [REQUIRED]
            String that contains the name of the alias to be modified. The name must start with the word 'alias' followed by a forward slash (alias/). Aliases that begin with 'alias/aws' are reserved.
            

    :type TargetKeyId: string
    :param TargetKeyId: [REQUIRED]
            Unique identifier of the customer master key to be mapped to the alias. This value can be a globally unique identifier or the fully specified ARN of a key.
            Key ARN Example - arn:aws:kms:us-east-1:123456789012:key/12345678-1234-1234-1234-123456789012
            Globally Unique Key ID Example - 12345678-1234-1234-1234-123456789012
            You can call ListAliases to verify that the alias is mapped to the correct TargetKeyId .
            

    :return: response = client.update_alias(
        # The alias to update.
        AliasName='alias/ExampleAlias',
        # The identifier of the CMK that the alias will refer to after this operation succeeds. You can use the key ID or the Amazon Resource Name (ARN) of the CMK.
        TargetKeyId='1234abcd-12ab-34cd-56ef-1234567890ab',
    )
    
    print(response)
    
    
    """
    pass
