How to Delete 'Un-needed Account?'

Hi:
In the past, I created three different Users' Account, however I deleted
two of accounts, leaving only Administrator, me and Guest Account by
accessing, .... Control Panel - User's Account.

However, there is still one of Accounts surfacing everytime I installed
devices, such as new Printer and even created new program, as "Owner,' even
though I'm the one who is 'Owner/Administrator.'

When I attempted to delete this Account by accessing, .... Computer -
Document - Users, .... it says, ... other person/user is still using ....
popping up in the middle of 'deletion' on this account, thus there is still
this account active because I'm unable to delete this particular account.

My question is;
How to delete 'un-needed Account' successfully?

Thanks for your help in advance.