How do you unlock old jerseys in mlb 2k10 for Wii?

To unlock old jerseys in MLB 2K10 for Wii, you need to complete specific challenges in the game's "My Player" mode or achieve certain milestones. Additionally, some jerseys can be unlocked by playing through the season and reaching particular accomplishments. Keep an eye on the in-game notifications for any unlockable content as you progress.