Trying to loop to beginning of program

I don't know how to get the program to restart if the wrong input is given.

I am new to java and don't know how to effectively use if statements or loops.

import java.util.Scanner; 

public class TuitionRates 
{
public static void main(String[] args) 
{
    //variables
    String name = "";
    String studentType = "";
    int creditNumber = 0;
    double totalTF = 0.00;
    double studentACTFee = 4.60;
    double parkingFee = 2.00;
    double tuition = 180.40;
    double capitalFee1 = 0.00;
    double capitalFee2 = 21.00;
    double perCreditR = 187.00;
    double perCreditV = 187.00;
    double perCreditD = 187.00;
    double perCreditM = 208.00;
    double perCreditB = 268.00;
    double perCreditO = 387.25;

    Scanner input = new Scanner(System.in);

    //Asking user for Name
System.out.println("Welcome to the NOVA Tuition and Fees Calculator.");
System.out.println("Please enter your name: ");
name= input.nextLine();

//Ask user to choose option

    System.out.println("Please enter the type of student that your are from 
    the choices below:\n"
            + 
            "R for Virginia Resident\r\n" + 
            "M for Military Contract Out-of-State\r\n" + 
            "V for Military Veterans and Dependents\r\n" + 
            "D for Dual Enrolled\r\n" + 
            "B for Business Contract Students\r\n" + 
            "O for Out of State Students\r\n");

    studentType = input.nextLine();
if (studentType.equalsIgnoreCase("R"))
   {

   System.out.println("Please enter the number of credits that you are 
   taking:");
   creditNumber = input.nextInt();

if (creditNumber <= 18)
{
System.out.println("Tuition and fees report for " + name);          
System.out.println("Tuition: "+ tuition);           
System.out.println( "Capital Fee:  \t"+ capitalFee1);           
System.out.println( "Student Activities Fee: \t "+   studentACTFee);            
System.out.println( "Parking Infrastructure Fee: \t " +  parkingFee);           
System.out.println("Tuition & Fees Per Credit: " +  perCreditR);            
System.out.println("X Number of Credits: " + creditNumber);
totalTF = creditNumber * perCreditR;            
System.out.println("Total Tuition and Fees: \t" +  totalTF);
System.out.println("Bodly NOVA");
}

else {System.out.println("Please re-enter credit Number ");}
}

I want my program to restart the if statement if the number of credits is over 18. So if I entered 19 it would say re-enter credits and start the if over.