As per the business rules
XVII. ELIGIBILITY TO APPEAR IN JEE (ADVANCED) IN SUBSEQUENT YEARS
58. Candidates who reject allocated seat can appear for JEE (Advanced) 2016 provided they meet all other eligibility requirements.
59. Candidates who accept the allocated seat by reporting at the admitting institute or a reporting center, irrespective of whether they attend classes or not, become ineligible for JEE (Advanced) in subsequent years.
60. Candidates whose admission is cancelled for any reason whatsoever become ineligible to appear to JEE (Advanced) in subsequent years.
61. Candidates who produce forged documents or indulge in acts of cheating are debarred from appearing in JEE (Main) and JEE (Advanced) next [and subsequent] year(s).
Also it says
40. Option to reject (or not accept) the allocated seat: Candidates who want to reject the allocated seat can do so as follows:
(i) By NOT remitting the seat acceptance fee [and hence, not report at the reporting center]
(ii) If the seat acceptance fee has already been remitted, by not reporting at the Reporting Center. Seat acceptance fee will be refunded to such candidates.
41. There is no option to withdraw from seat allocation or to surrender an allocated seat other than by rejecting the seat as mentioned above
42. Candidates who reject allocated seat cannot participate any more in Joint Seat Allocation for the ensuing academic year 2015-16.