Admin unable to delete standard user account -14120 (eDSPermissionError)

I am trying to re-configure user administration on an older MacBook Pro without having to factory reset. I'd like to preserve the applications. Its running High Sierra currently.

• I was successfully able to create a new admin account with my Apple ID
• I was able to successfully delete the previous admin account
• There's one other standard account I'm trying to delete that I can't. Its asking for that users password and we can't remember it.
• I tried to delete it from terminal using sudo /usr/bin/dscl . -delete /Users/ and its giving me the error DS Error: -14120 (eDSPermissionError)

My account is an admin account, I would think that running the sudo command would work. Any suggestions would be appreciated thanks!