When you don't know the username and password or you need to change them, you can use IPMITool to perform this task along with other user management tasks from an SSH terminal windows, like PuTTY.
Listed below are the user management commands I found helpful.
Listing the iDRAC User
Command:
ipmitool user list 2
Example:
[root@APPLIANCE14 ~]# ipmitool user list 2
ID Name Callin Link Auth IPMI Msg Channel Priv Limit
2 root true true true ADMINISTRATOR
Enabling the iDRAC User
Command:
ipmitool user enable 2
Example:
[root@APPLIANCE14 ~]# ipmitool user enable 2
Disabling the iDRAC User
Command:
ipmitool user disable 2
Example:
[root@APPLIANCE14 ~]# ipmitool user disable 2
Set the iDRAC User Password
Command:
ipmitool user set password 2 <Password>
Example:
[root@APPLIANCE14 ~]# ipmitool user set password 2 themaster01
Rename the iDRAC Root User
Command:
ipmitool user set name 2 <newusername>
Example:
[root@APPLIANCE14 ~]# ipmitool user set name 2 bueno
[root@APPLIANCE14 ~]# ipmitool user list 2
ID Name Callin Link Auth IPMI Msg Channel Priv Limit
2 bueno true true true ADMINISTRATOR
Full List of Options for 'ipmitool user'
[root@APPLIANCE14 ~]# ipmitool user set name
User Commands: summary [<channel number>]
list [<channel number>]
set name <user id> <username>
set password <user id> [<password>]
disable <user id>
enable <user id>
priv <user id> <privilege level> [<channel number>]
test <user id> <16|20> [<password]>