See how much interest and how many months you save by part-prepaying a loan, and compare reducing the tenure with reducing the EMI.
Month by month: interest = balance × r; principal = EMI − interest; then any prepayment is subtracted from the balance. Reduce-tenure keeps the EMI until the balance reaches zero; reduce-EMI recalculates the EMI on the new balance over the remaining months.
₹10 lakh at 10% for 20 years with a ₹2 lakh prepayment in month 24 (reduce tenure) saves over 4 years of EMIs.