Progression relies heavily on entering events, winning prize money, and spending that capital inside the car parts shop to build progressively faster builds. Anatomy of the "T-En by M. Z. v0.01" Patch

you can upgrade in the game, or are you looking for a guide to apply the patch Choro Q 3 (Fan Translation) - LongPlays.org

Do not play this for the story. Play this to feel the clunky, adorable charm of late-90s Japanese racing RPGs with life support. You will win races through trial and error, not dialogue trees.