Agree with The Greek, practice parts of the song individually and try to get them up to tempo, rather than the whole song. When you've either sussed a section (or got it a bit quicker than it was), move on to another section and so on. Then when you're comfortable with it play a couple of sections together and build up to the whole song. Don't rush it, and more importantly, don't overdo it either. Take say 5-15 minutes or so on one part, have a wee break, move on to the next part for another 5-15 minutes or so. Put the parts together and go over them for another 5-15 minutes. Build slowly.