Xbox Live
Xbox Live is the online gaming community for Xbox 360 owners. In addition to downloadable movies, music and game previews, bonus material is available for a variety of games, including 2K9. Usually updates are applied automatically once the game is loaded --- an on-screen prompt tells you of the update's nature and progress. All you need to access rosters is a valid Xbox Live account and a paid Gold membership, a monthly service that allows users to play online and receive all the latest add-ons for Xbox games.
Updating the Roster
If the roster doesn't automatically update once you've loaded the game, press the center button on your Xbox controller to access your Live Dashboard. Scroll over to Games, where you'll be able to browse content for a host of Xbox titles, including 2K9. Select "M" for titles beginning with the letter M. Scroll down the list to find MLB 2K9; highlight the title to access its content. Select "Game Add-ons" from the menu. There should be a roster update that you can click to access. Updates are usually free.
Manually
From time to time, Xbox swaps out content. In the case of MLB 2K9, newer roster updates are included to reflect the current game's status. As of August 2011, "MLB 2K11" is the most recent game. This shouldn't hamper players looking to update rosters. Although it's a painstaking process, manually swapping players from team to team can be done before an in-game season to avoid dealing with the game's salary cap. Log on to MLB.com, the official site for all the teams currently in Major League Baseball, for all the roster information.
Troubleshooting
Occasionally, problems can arise. For example, you can't log on to Xbox Live, the automatic download is refused or you are not able to download the new rosters. If this happens, check your connection, your wireless router or your hard drive. Chances are something is amiss with your connection, your Live account or you don't have any room on your hard drive or auxiliary memory device to accommodate the update.