replace default farm administrator

How can we replace default farm administrator to any other account or vice - verse ? Please let me know the steps required to perform this task if possible or if not possible please provide an alternative.

Even though it's possible it's not a good idea doing that, I'll recommend if possible to reinstall SharePoint, do it again, do it right!

However if you decide to change it, here is the instructions, they are provided without any guarantee!

Go to Central Administration -> Security, click the Configure Service Accounts link under General Security head. Then select Farm Account from the doprdown list. Make sure the account you use have all the permissions. You need those permissions:

The server farm account is used to perform the following tasks:

Configure and manage the server farm.
Act as the application pool identity for the SharePoint Central Administration Web site.
Run the Microsoft SharePoint Foundation Workflow Timer Service.

Type av account:
Domain user account.

Additional permissions are automatically granted for the server farm account on Web servers and application servers that are joined to a server farm.

The account is added to the following SQL Server security roles:

dbcreator fixed server role
securityadmin fixed server role
db_owner fixed database role for all SharePoint databases in the server farm