Indian railway has launched latest up-gradation system of sleeper class ticket 3rd ac class and 3rd ac class to 2nd ac class. This system is very useful for all passenger. In this system passenger pay for only those tickets which is booked by him. In this system if upper class birth is not fully booked then the seats are booked from those passengers who have confirm ticket of lower category class.
In this system any extra charge taken from passengers.
For example if you have confirm ticket of sleeper class then your ticket will be upgrade to 3rd AC class. If you have confirm ticket of 3rd AC class then your ticket will be upgrade to 2nd AC class.
If you book your ticket for off season then you have to big chance for upgrade your ticket.
The another way of upgrade your ticket book your ticket before at least 20 days of your journey.
But it is necessary for upgrade the ticket that the seats in upper class should be available. If seats in upper class is unavailable then your tickets would not be upgrade for upper class.
For know your upgrade status send your PNR number as SMS to 139 before 1 hour of your train time schedule.