TFS - Change TFS server's service account
Use ChangeAccount to change account and password settings for all service accounts.
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The following example shows the syntax used to update service accounts. The utility swaps all instances of the old account, MyOldAcct, with a new account, MyNewAcct, and new password, newPass. The utility iterates through the services and only changes those which run under the old account.
>TFSAdminUtil.exe ChangeAccount MyOldAcct MyNewAcct newPass
For more detail info, please refer to the following URL:
http://msdn2.microsoft.com/en-us/library/ms253107(VS.80).aspx
Attention: please backup the TFS databases before you did it.