I'm assuming you are talking about the orbital period of the Earth? Years do change as we change definitions of time, although these are small.

The Earth is actually moving very slowly away from the Sun, so years are getting a little longer, although the difference is pretty difficult to measure.

The Sun pushes the Earth away due to the solar wind, but this actually has very little effect. More important is the mass loss by the Sun via the solar wind (and fusion reactions). The Sun loses a mass of about 8 Earths per year. One site I saw said this has resulted in a net loss in velocity of 22 m/s over the life of the solar system--fairly insignificant to the current 29.78 km/s

If you go back far enough, then the Earth was involved in major collisions. These could have had great effect on the orbital period by (mostly) adding large amounts of mass.