Norman it's called practice, do not try and play it's normal speed slow it right down, take each bar at a time, or the bars that you are having most
difficulty with slowly then gradually speed the song up to it's normal tempo.
It might take you a couple of hours to learn it or a couple of weeks/months it does not matter, if you like the song that much you will probably learn it quicker...just practice practice practice,
some people are gifted like pianoman who can listen to a song and within a couples of hours do a great rendition of it, others take longer, there is no real short cut it is down to the individuals skills and music knowledge.
hope that helps
Regards Del