Temperature sensor reading is higher than the actual temperature // Tells the Arduino to read A2 and stores the value in “Vin”    
Vin = analogRead (tempSensor); 

// Converts the voltage value to temperature and stores it into the “TC” variable (in °C)
TC = 500.0 * (Vin / 1024.0); 


The temperature shown is about 50.25°C, sometimes it is showing 36-38°C   degrees, but the actual temperature is about 25-26°C.

Why this is happening?

Code:

Vin = analogRead (tempSensor);
TC=(500.0*Vin)/1023.0;
TF = ((9.0*TC)/5.0)+32.0;
lcd.setCursor(0, 1);
lcd.print(TF);
lcd.print((char)223);
lcd.print("F ");
lcd.print (TC);
lcd.print((char)223);
lcd.print("C");
delay(1000);
Any chance you're printing Vin, and not TC? 

500*(50.25/1024) = ~24.5

If not, please post as much of your program as possible