If you have 30 hours of flying experience within the last 3 years you can straight away renew for lifetime without giving any exams and by paying the 10,000 rupees DD
If you dont have 30 hours of flying then you need to pass Part 1 again . On the first post of this thread i have given link for last dates to apply , dd details etc for the December hyderabad attempt
The application window usually opens 2 weeks prior to the last date to file online
P.S : I have heard that if you have 30 hours of flying after the RT was issued . Then irrespective of the 3 year rules you can still renew the RT for lifetime . I am not sure how true it is , but I have a friend trying out this method . If its successful then I'll report back here and let everyone know