Upgrading MSTW Team Rosters to version 4.0 from an earlier version is not as simple as pushing the WordPress upgrade plugin button, but it’s not hard if you follow the steps listed below. NOTE these steps are not necessary for a new installation, use them only if you want to move existing data from version 3.1.2 to version 4.0.

• BACKUP YOUR SITE. This is good practice for any WordPress core, theme, or plugin update. Better safe than sorry!
• If you have customized the plugin’s stylesheet (css/mstw-tr-style.css), MOVE IT to a safe location. It WILL be overwritten in the install process. (BTW, this issue has been resolved in version 4.0.)
• Remove the single-player.php and taxomony-teams.php from your theme’s or child theme’s home directory IF you have copied them to there. Move them to a safe location if you have customized them for your theme.
• Install the MSTW CSV Exporter Plugin (VERSION 1.2 or higher).
• Export your existing team and player data tables using the MSTW CSV Exporter. This process is important in order to migrate your existing data to the new data structures.
• Install version 4.0 of the MSTW Team Rosters plugin.
• Use the CSV Roster Import admin screen to import the teams table, then the players table. There are two important settings for the Players import, please read the CSV Import man page before importing the players.
• Do NOT re-install your customized stylesheet. First, the file name has changed. Second, you can now add your customizations without changing the plugin’s default stylesheet. Please read the Customizing the Team Rosters Plugin man page for the details.