If you are asking for Jee main then the better marks would be considered and there is no issue in giving improvement in less than 5 subjects as it is valid if the attempt is for getting the requisite 75% in Class 12.
To know about the same in detail, you can go through the below link-
Jee Main eligibiity 2018
Good Luck!!!
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile