change dbo user to windows login name

I am trying to add a windows user to a database in Security of that database but I am getting the error " The login already has an account under a different user name so when I  check this windows user,this windows login name exist as dbo user name like attached file so how do we change this dbo user to windows login name?
Teoman SahinAsked:
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Anoo S PillaiCommented:
The mentioned windows login is already mapped as dbo ( database owner ) .  If you want to map the windows login as a separate user in the mentioned database, first you should map another login as dbo ( database owner). To do this from script, the procedure sp_changedbowner can be used.

Use   <<YourDBName>>
sp_changedbowner '<<SomeotherLoginName>>'

( If you want to do from SSMS interface, then Right Click on database ->> Properties ->> Select Files Page ->> Change the owner by clicking on the button adjacent to Owner text box ) .

Then you would be able to map windows login.

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Teoman SahinAuthor Commented:
I have already changed the owner to domain\xyz user from Properties ->> Select Files Page ->> Change the owner by clicking on the button adjacent to Owner text box but when I check the Security of that database, I am still seeing the dbo user and in properties of dbo

login name= domain\xyz

so we have to change username=dbo to domain\xyz
how to map it?
Anoo S PillaiCommented:
1) If you are using mixed authentication, can you try sp_changedbowner from SSMS Query windows and post the response from SQL server- , as well the

Use   <<YourDBName>>
sp_changedbowner 'sa'   -- or any other SQL login

2) BTW, what you are trying to achieve by this ?
Anoo S PillaiCommented:

I think that you did a good amount of extra work to resolve the problem from the grading provided. Could you please post a short note on the actions that you have taken to resolve the issue..

That would be a reference for future.

Thanks in advance,
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Microsoft SQL Server 2008

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