Purchase the sheet music. You can find this song at local music stores, or online. It is available for download at a variety of websites, including Karashome.boo.pl. (Karashome.boo.pl)
Learn the Right Hand or treble staff component of the song. This can take some time as it is a lengthy piece. Break up the music into sheets and spend equal amounts of time per line. It is important to get quality, not quantity, when it comes to learning music. The right hand has much of the melody in this song and is therefore vital to making the end result tasteful and similar to what you have heard in the past.
Practice the left hand bass notes. There are some patterns to the music in the left hand, especially in the arpeggios. Be sure to practice them slowly, as it keeps the tempo of the whole song.
Put both hands together. This will take just as much time as learning them separately, but is important. Take your time and slowly add in the dynamics. Generally, the left hand should be slightly softer than the right, except when it takes the melody for brief moments throughout the song.
Listen to the song online or on the movie. Get a feel for how it should sound and practice your music so that it sounds similar. Keep in mind that there is frequently a great deal of other sound editing involved with a finished product, but the general theme should stand out even when you play.