The current version of Game Schedules was developed and tested one WordPress 3.7.1. If you use older version of WordPress, good luck! Much of the plugin was originally developed on 3.4.x so that might work okay. (No guarantees.) If you are using a newer version of WP, please let me know how the plugin works, especially if you encounter problems.
Upgrading to this version of Game Schedules should not impact any existing schedules. (But backup your DB before you upgrade, just in case. NOTE that it will overwrite the css folder and the plugin’s stylesheet – mstw-gs-styles.css. So if you’ve made modifications to the stylesheet, you may want to move them to a safe location before installing the new version of the plugin. Also, you should test your display settings; some may need to be reset. An effort was made to change as little as possible, but the display settings may not be 100% backward compatible.