How do I code my program, so the strings I have in my arraylist are actually removed?

import java.io.*;
import java.util.*;
public class LoginPagev2
{
	public static void main(String[] args) throws IOException
	{
		String answ;
		String user;
		String pass ;
		int counter = 0;
		Scanner keyboard = new Scanner(System.in);
		System.out.println("Welcome! This program will allow you to sign in with a username and password you created.");
		System.out.println("If you fail to login correctly 3 times, this program will terminate. You can only sign in once per username.");
		System.out.println("If you wish to sign in into the same account twice, you must restart the program.");
		while(true)
		{	System.out.print("Would you like to sign in? (Y/N): ");
			answ = keyboard.nextLine();
			if(answ.equalsIgnoreCase("N"))
			{
				System.out.print("Goodbye!");
				System.exit(0);
			}
			System.out.print("What is your username?: " );
			user = keyboard.nextLine();
			System.out.print("What is your password?: ");
			pass = keyboard.nextLine();
			while((!list().contains(user) || !list().contains(pass)) || counter < 3)
			{
				++ counter;
				if(list().contains(user) && list().contains(pass))
				{
						list().remove(user);
						list().remove(pass);
						System.out.println("Congrats! You successfully signed in!");
						counter = 0;
						break;
				}
				if(counter==3)
				{
					System.out.println("You have attempted you max amount of tries. This program will now end.");
					System.exit(0);
				}
				else
				{
					System.out.println("This is not valid. Please try again");
					System.out.print("What is your username?: " );
					user = keyboard.nextLine();
					System.out.print("What is your password?: ");
					pass = keyboard.nextLine();
				}
			}
			System.out.print("Would you like to sign in with another account? (Y/N): ");
			String rep = keyboard.nextLine();
			if(rep.equalsIgnoreCase("N"))
			{
				System.out.print("Goodbye!");
				System.exit(0);
			}
			else
				continue;
		}
		
	}			
	
	public static ArrayList<String> list() throws IOException
	{
		try
		{
			BufferedReader reader = new BufferedReader(new FileReader("loginInfo.txt"));
			String line;
			ArrayList<String> arr = new ArrayList<String> ();
			while ((line = reader.readLine()) != null) 
			{
				arr.add(line);
			}
			reader.close();
			return arr;
		}catch(Exception e)
		{
			return null;
		}
	}
	
}