Get an invitation. Unfortunately, attendance to the Academy Awards (Oscars) is by invitation only. So either become an actor or try to be an actor's date. Or become an entertainment reporter or a paparazzo so you can work the occasion.
Sign up to be a seat filler. A seat filler fills the seat of a person who leaves the theater. The producers of the Academy Awards want the theater to always look full for the wide camera shots, thus they hire seat fillers.
Sleep on the sidewalk in order to sit on the bleachers that line the entrance to the theater. Or you could stand in the roped section along the red carpet to see your favorite stars. Although this would not count as attending, you will still get the chance be near the red carpet.
Attend film school or get a job in the film industry. Then one day you could possibly attend the Academy Awards and even take an Oscar home.