Sir i have given 12 class CBSE exam in 2013 with 77.6% and in iit advance i secured 97%tile but due to cut off mark in 12 class (78.2%) I am not eligible for IIT this year

Now i decided to reappear in 12 class & prepare for IIT from kota again, i have given 12 class exam from kota, i have few queries related that

1. can i give 12 class exam from other school?

2. can i change my board exam? (from CBSE to UP board )

3. can i appear as a fresher student for 12 class?

Sir its very helpful if u guide me.

Thanks You