Sql server 2008. it's said it's applicable without restarting the
instance.

but I just cannot find a way to change the password in the
configuration manager?

There should be something I've missed, can anybody tell me? Thank you
very much!

When you select SQL Server Services, just double click on the instance service (or right click and select Properties)
and there you can change the service account credentials.

--
Plamen Ratchev
http://www.SQLStudio.com