Slow but steady goes the turtle... You cannot learn to play all the notes overnight. Start in the middle of the staff and practice exercises in that area. Over time expand the range of your exercises up a half tone, and down a half tone. As you get comfortable, expand some more, a half tone at a time. In a few years you will be playing from low F# to high G, and in a few more you will be playing even higher. Being in a hurry won't do it. Slow and steady wins the race.