RbkMan
You can use this Command Line Interface guide. Page 94 and 95. This is for CUCM 11.0, but it has not changed much through the iterations in regards to this. I don't know what version you are using. If the Admin, Application and Security password are not what you are looking for, you can use the GUI and go to User Management>>>Application User and select the user you want to change and change it there. If you have locked yourself out of the OS and DRS, because you don't have the Administrator account password that was created during install you need to go through password recovery. Use this link from Mohammed al Baqari which will tell you everything you need to know and mark his post helpful if it works for you.
https://community.cisco.com/t5/collaboration-voice-and-video/cucm-passwords-and-password-recovery/ta-p/3162863
Command Line Interface Reference Guide
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/cli_ref/11_0_1/CUCM_BK_C93262BC_00_cucm-cli-reference-guide-1101.pdf