Short answer: no, not directly. Once your ticket is confirmed, IRCTC gives you no way to change the berth or the berth type on it. There is no 'modify berth' button, and there never has been.
That is not the end of it, though. There are three things that do work, and one popular idea that usually backfires.
What doesn't work: cancelling and rebooking
This is the first thing most people try, and it is usually a mistake. You pay cancellation charges, you lose your confirmed status, and you rejoin the queue at whatever availability exists now — which on a busy route means waitlist.
You are trading a confirmed upper berth for a real chance of no berth at all. It is only worth considering when the train is genuinely empty and you can see availability before you cancel.
What works: asking the TTE on board
After the chart is prepared, the TTE has a live picture of which berths are actually empty — no-shows, late cancellations, passengers who boarded elsewhere. They can allot those.
This is real and it happens on every train. The catch is in the word 'vacant': on a fully booked train there may be nothing to give. Ask politely once the train is moving and the TTE has finished the first round of checking.
Priority goes to those who need it most. Ticket-checking staff are specifically directed to allot vacant lower berths to senior citizens who have been given a middle or upper berth.
What works: the lower berth quota, if you plan ahead
This one only helps before you book, but it is worth knowing for next time. Senior citizens, women aged 45 and above, and pregnant women are allotted lower berths automatically where they are available, in sleeper and AC classes.
IRCTC also offers a 'book only if lower berth is allotted' option at booking. If a lower berth is genuinely the point of the trip, that setting is more reliable than hoping.
What works best: swapping with a co-passenger
This is what most people actually end up doing, and on a full train it is the only option with a real success rate.
The reason it works is that berth preference is not universal. Plenty of travellers prefer an upper berth — you can lie down whenever you like, nobody sits on your bed during the day, and there is no traffic past your feet. Someone with a bad knee and an upper berth, and someone who wants to be left alone up top, both come out ahead.
Nothing about your ticket changes. Your PNR, your coach and your berth number stay exactly as booked; you simply occupy each other's berths. TTEs generally do not object to a consensual swap within the same class, and many will not even be aware of it.
The hard part has never been the rule. It is finding the person. Ask around your bay and you have reached about six people, only after you have already boarded — and the passenger who would happily have traded is two coaches away.
Common questions
Can I change my berth on the IRCTC website after booking?
No. IRCTC provides no option to change the berth or berth type on a confirmed ticket. Berth preference can only be given at the time of booking, and even then it is a preference rather than a guarantee.
Can the TTE change my berth?
Yes, if something is vacant. After chart preparation the TTE can allot empty berths, and is directed to give vacant lower berths to senior citizens first. On a fully booked train there may be nothing available.
Will I lose my confirmed seat if I cancel and rebook?
Very likely on a busy route. You pay cancellation charges and rejoin the queue at current availability, which often means a waitlist. It is rarely worth it purely to change berth type.
Railway rules change from time to time and a lot is left to the discretion of on-board staff. Treat this as a traveller's guide, not an official ruling — check with Indian Railways or IRCTC if something matters to your journey.