P4 or P5 which subject to do

The best is to look at a few of the recent exams for both papers (you can find them on the ACCA website).

Then you will see the style of the questions and the sort of knowledge required. Since you were exempt from F5 and F9, you obviously did cover the topics at college.
Looking at these recent papers will let you form a judgement as to how much you remember, how much you understood the topics at college, and therefore which you are likeliest to find the most easy.

OK. Come back to me on here if you are still uncertain 🙂

Work through all the lectures and course notes on here; refer back to F9 lectures if you find anything that you had forgotten from F9; refer to your Study Text on anything you are not sure of from the lectures; but most of all practice and practice.

You must get a Revision/Exam Kit from one of the approved publishers and you must work through every question properly. If you come across something you don’t understand then ask in the Ask the ACCA Tutor Forum.

Certainly you must work through the past questions and answer from the ACCA website.

The problem is that there are only a limited number of exams on there, and the more practice you get the better. By far the best way of really learning for the paper is to practice lots and lots of exam standard questions.
The Revision/Exam Kits have loads of them, and for that reason it really would be sensible to get hold of one of them so that you can practice lots of questions – not just the recent past exams.