In the client/lead or contact tab there is a field that associates the "owner" of contact/lead etc. 

It is the username of the account. So now I only have 1 username, but there is an option to change that which is 

useless as there is only one account under my CRM now. 

This was not possible few days ago but it suddenly appear. 

Is there a way to disable the function "change" in terms of changing the owner of the contact or client entry in the client / contact owner field?

Thanks, hope you understand the question. 

I attached the picture. 

thanks a lot!