Login to Central Admin server and open SharePoint Management Shell as administrator.
Run the below command (Replace Credentials with your new Credentials of the farm)
stsadm -o updatefarmcredentials -userlogin sp\<Account Name> -password <Account Password>
Have Fun :)
Run the below command (Replace Credentials with your new Credentials of the farm)
stsadm -o updatefarmcredentials -userlogin sp\<Account Name> -password <Account Password>
Have Fun :)