Hi Jyothi,
if you need to perform any change to the standard smartform first of all you need to analize the field that you should change and wich value will be the correct one and also if this value is available.
After you have this details, you should change the smartform and assign the new smartform in customizing in order to use this new one instead of the standard one.
this may help .> http://wiki.sdn.sap.com/wiki/display/SRM/Customizing+Standard+SRM+Smartforms
Please let me know if you need further details,