You will come across this situation where the customer forgot the CUCM GUI Admin username or password or both. In that case you can still login to CUCM GUI by adding another user from CUCM CLI.
SSH to CUCM – the Administrator ID can not be changed once you have set it during Installation. This is the same ID which is used to get SSH access to CLI of CUCM. Most people normally set it to ‘Administrator’. This is different from CUCM GUI access which can be an id like ‘ccmadmin’ or ‘ccmadministrator’ or could be anything. This id cannot be changed once set but the password can be changed from CLI.
CLI> Set Password Admin
The Application user for GUI access say Administrator can be changed. When I say ‘changed’ that does not mean you can change the previous GUI Application user but what I mean is that you can add another user for GUI access and then you can either reset the password of previous application user from GUI or delete it from there after making the new one.
This is how you can create a new GUI application user:
CLI > utils reset_ui_administrator_name
CLI > utils reset_ui_administrator_password
The previous username will remain there and it will not be deleted or amended until you delete/amend it from CUCM>Application User GUI.
voiceonbits.com 
Thank you so much for this information , not a single person in Cisco forums could provide this simple solution. So many course also do not provide this simple explanation
I feel unlucky that i didnt find this webpage for this long. The solutions you provide are not more than 10 lines. Keeping as simple as possible. Appreciate the work bro.
saved my life, many thanks!