From now, for my opinion, I don't suggest you to study any kind of book. You should find some piece to practise your slef, such as: Chopin's importus......Beethoveens....Tchaikovsky's piano concertos.
If you get a self practise correctly, I am sure that you will get a big improvment.
After that, you can try to take the exam of ABRSM's diploma.
^ ^ You may think about this yourself. ^ ^
^ ^ Hope my suggestions may help you ^ ^