Kindly do not update any train to modify the coach compositions. Simply go to the train page and you shall find a link to the right saying 'change train classes'. Click there, make the changes and click on submit.
Also try avoiding overwriting admin notes and coach compositions unless it is absolutely necessary.
In such cases, it is advisable to merge the previous...
more... admin notes and coach compositions if the situation demands so.
For example, I saw that Goyal Sir had updated the admin notes of Deccan Queen saying that it does not have a Pantry Car but has a Dining Car. Such notes should be retained and not pushed down for others to find it out from the 'Admin Notes' link.