Please check with your college for the latest guidelines.
Mumbai University offers an option called Class Improvement Scheme (CIS) which allows those who have passed to give the exams again to improve their percentage.
Although technically anyone can avail of this scheme, the ultimate approval is in the hands of the principal of one's college. One must submit a written application to them, which (to the best of my knowledge) is usually never rejected. After approval is obtained, one may fill up the exam form.
You have a maximum of 2 attempts to improve in the two exams that immediately follow your first attempt - the October exam of the same year, and the March exam of the next year. You can't give the class improvement exams after any gap.
Note that one has to writethe papers again, not just the ones in which one has scored low.
I do not think that one has to reappear for the practical exams. However, do check with your college to make sure.