Install another FIFA 13 on your HDD! Tutorial here: http://www.fifa-infinity.com/board/viewtopic.php?f=69&t=496
In case you don't want to add another FIFA 13 to your HDD then backup your main FIFA13 files!
After you've prepared your new FIFA 13 like in the tutorial link follow the next steps:
1) Run the setup file of FIFA Futsal 13 and install it in the main FIFA13 folder of your new FIFA13.
2) When the regenerator pops out, right-click on it and set the path to your new FIFA 13 folder where you installed the mod and click GO.
3) The regeneration process will take a while! After it's done exit the regenerator!
4) Click on the new FIFA Futsal 13 exe shortcut on your desktop and enjoy the game!
* To enable the 7 vs 7 mode please follow the Cheat Engine tutorial in the other Read Me file!