How to change value in SQLite database?

I am learning android and building a rather big project. My goal is to let the user change their Email address onClick in the MainActivity, but I can't figure out how to change a value in the database.

I know it should be something along the lines:

db.update(TABLE_NAME, cv, where, value);

The problem is that the database is defined in the SQLiteHandler class, but I can't figure out how to use the same "db" in the "update" code. I keep getting "Cannot resolve method.." on the db.update.

I tried copying

 SQLiteDatabase db = this.getWritableDatabase(); 

to my MainActivity, but at this point I'm lost.

I followed this tutorial for the registration system.

My code so far:

private static final String TABLE_NAME = "email";

btnChangemail.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            db = new SQLiteHandler(getApplicationContext());
            HashMap<String, String> user = db.getUserDetails();


            String email1 = user.get("email");

            String s1 = etChangemeil.getText().toString();


            ContentValues cv = new ContentValues();
            cv.put(user.get("email"), s1);

            String where = (user.get("email")) ;
            String[] value = { email1 }; 


            db.update(TABLE_NAME, cv, where, value);
        }
    });

Best regards,

Dan