Never mind, I got it.
I will just add the solution here.
First login as an admin user which you don't want to delete. Then :
> Go to System Settings
> Open Users & Groups
> Click on edit on Network account server
> Authenticate(if asks) & click on "Open Directory Utility"
> Go to Directory Editor
> There will be a lock icon just below Directory Editor text if you have not authenticated just click on it & write the username & password & authenticate
> Scroll down look for Name of the user(not User Name for me it was Rohit Kumar even though my username was different)
> Click on it & check the record name if it matches with the username you want to delete
> There will one "+" & "-" icon at the bottom. Click on "-" & remove.
This is it. Hopefully this will help you. Thanks.