您不能更改用户名.您可以检查以下链接,描述如何更改主密码,如果亚马逊添加了更改您将在那里找到的用户名的功能：
尝试在AWS CLI for RDS找到：
modify-db-instance --db-instance-identifier <value> --master-user-password (string)
–master-user-password(string)
The new password for the DB instance master user. Can be any printable
ASCII character except “/”,“””,or “@”.
Changing this parameter does not result in an outage and the change is
asynchronously applied as soon as possible. Between the time of the
request and the completion of the request,the MasterUserPassword
element exists in the PendingModifiedValues element of the operation
response. Default: Uses existing setting
Constraints: Must be 8 to 41 alphanumeric characters (MySQL,MariaDB,
and Amazon Aurora),8 to 30 alphanumeric characters (Oracle),or 8 to
128 alphanumeric characters (SQL Server).
Amazon RDS命令行界面(CLI)已被弃用.而是使用AWS CLI进行RDS.
通过AWS Management Console,选择您需要重置密码的实例,单击“修改”,然后选择一个新的主密码.
If you don’t want to use the AWS Console,you can use the rds-modify-db-instance command (as per Amazon’s documentation for RDS) to reset it directly,given the AWS command line tools: rds-modify-db-instance instance-name –master-user-password examplepassword
