First you have to get at least 30 paint brushes (you can use the duping cheat to get them).
Then you need to walk to the arena in the Imperial City set down a paint brush and jump on it. Repeat this process until you are at the top of the arena, then jump to the center of the arena and there you go.
P.S you don't have to save before you do this because there is a door that you can select and it will take you to the inside of the arena.