Changing optional paper

Hello guys. I am thinking about changing optional paper, more precisely from APM (P5) to AFM (P4). This is due to my disastrous attempt of APM yesterday after being completely irrelevant on a 15 mark question in section b. Am only left with P4 to qualify. Can one cover P4 syllabus for dec 20 attemp if i start now? Please advice. And also which Provider ( bpp and Kaplan) gives you a more comprehensive overview of the syllabus? God bless you all.