Using STSADM (all PS 2007 Service Accounts incase using the same account):

1.     Change the account password

2.     Open a command line prompt (Start -> Run -> cmd)

3.     Change directory wherever STSADM has been installed, typically:

cd "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN"

4.     Execute the following two command:

stsadm -o updatefarmcredentials -userlogin DOMAIN\user -password NEWPASSWORD

stsadm -o updateaccountpassword -userlogin DOMAIN\USER -password NEWPASSWORD –noadmin

IISRESET

5.     Reboot the server.