adding new and changing sql management account

I have few SQL 2012 servers. A management account on these servers is AD basic user account: sqladmin that is a member of Local Administrators group on each server.

couple of questions:

1. if I will change the password for sqladmin in AD, where I have to change the password on SQL servers.

For each SQL service (in services) ? No option in Management studio? Or may be not at all on SQL servers?

2. On one SQL server (SQL 2008) SQL management account is member of Domain Admins group.

I want to replace it by existing for this purpose basic AD account: sqladmin.

How to proceed?

Thanks.

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