hello ashutosh 

Actually the percentile of a candidate depends upon vivid parameters like number of students appeared in the exam , no of students in total , marks scored by individuals etc.

one of the reasons for your change in percentile can be that in the exam batch you appeared for have many candidate scoring the same marks and in the other batch student appeared might be less and marks scored by them would have been less.As a result the overall percentile for the same marks have been given a higher percentile than other batch.  

Based upon the above criterias your marks is just a personal score you have earned in the exam, but when it comes to percentle score the same marks is compared with many other candidate and based upon other factors.

HAPPY LEARNING!!