As you want to appear for JEE (Advanced) 2013 examination, you must appear for the JEE (Main) 2013 first.
The top 150,000 candidates (including all categories) who qualify with their respective category wise cut-off scores in JEE (Main) 2013 are eligible to write JEE (Advanced) 2013.
You need to fill another application for JEE Advanced Between 8th May 2013 to 13th May 2013.
To know more about new format of JEE 2013, click on the links below-
IIT-JEE (Joint Entrance Examination) to Undergo Changes from 2013
COBSE to Share Percentage Requirements to be in "Top 20 Percentile" for IIT JEE 2013
Kapil Sibal's Latest Proposal for IIT-JEE's New Format
IITs Agree, IIT-JEE and AIEEE to Merge
All the best !!