My age is 23 years ..... height is 5 feet 3 inches ... weight is 75 kg. how much weight should i reduce ?

Approx. 20 KG: Usual suggestion re weight is approximately 100 lb for the first 5 feet of height and 5-7 lb, per inch above 5 feet. So around 55kg for 5 feet 3 inches.

Body mass index: We use body mass index (bmi) to categorize into underweight, normal, overweight & obese. 75kg=165lbs which gives bmi 29.2 using http://www.Nhlbi.Nih.Gov/guidelines/obesity/bmi/bmicalc.Htm which means overweight (obesity is >30). Need to drop down to 141 or 64kg to achieve bmi of 25 which is highest normal.