Simply, you've just got to memorise it! I just went through each line and repeated it out loud to myself. Once I was sure I had learnt it I moved onto the next line. It's a very long boring process but I got a good grade, so it was worth it! It's best to start learning it earlier and just go over bits everyday to keep it fresh in your mind. You will get faster the more you practise! Good luck!
I find that writing it out a few times helps, but make sure you've got it right before you start learning it. Then, start saying it out loud. I do it paragraph by paragraph and then try two paragraph's and so on until i have learnt the whole thing. I hope this helps, and I hope i'm not too late before your speaking exam! :)