Due to many reasons we used to shift server, as by going to new hosting

So do we have no make changes only in these two files

sites/default/constants.php and sites/default/config.php

Or there is any took like repair_settings in smf?

Please guide

you only need to change the host, username and password in sites/default/config.php file.
constants.php is used for internal reference and must not be changed.

So there is no need to tell path of attachment, avatars and other foloders?

No there is no need, path is computed automatically.