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@Spiker, as Bill Brown said, generally you use 1 finger per fret. In other words you cover 4 frets without moving your hand.
So the first fret would be your index finger, The second fret is your middle finger, the third fret is your ring finger, and the fourth fret is your pinky.
Assuming that is what you are doing, it may be just a matter of getting your hands looser. This will come with time.
In the beginning it is best to play as recommended. This will help develop good habits and build finger dexterity. However eventually you start recognizing your limitations or simply learn an easier way. When you get to that point there is nothing wrong with using a different fingering to accomplish what you want to play.