XP / VISTA USERS
Go to the Start Menu and click Run. Type in %appdata%.
Then click 2K Sports, then NBA 2K13.
Unpack content of this rar in that folder.

WINDOWS 7
Type %appdata% in your Start Menu's search bar and press Enter.
It will take you to your Roaming folder, where you can click 2K Sports and then NBA 2K13.
Unpack content of this rar in that folder.

Roster File Name : 3001.ROS