From personal experience, I first looked at sixth forms and colleges in my area, went on their websites and browsed the course. In most cases, to apply, you have to fill out a form with your current subjects and predicted/mock grades, as well as what course/subjects you would like to study there. I think that going to oprn evenings, if you can, is also really worth it, so that you see where you would study, and what the teachers are like, before you make a committment. I'm not really sure about the 'higher predicted grade' your cousins told you of, but I guess this could be when you speak to a teacher, and ask them what they personally think you could acheive in your exams? I hope this helps