first u need a usb flashdrive
plug the flashdrive into your pc then click on the flashdrive and open it up and create a folder inside it called PS3 then click on that folder and inside that type in SAVEDATA.
once u do that come here and u download a roster file onto your pc then once its on your pc go back your usb flashgdrive open it up and drag the downloaded roster file into PS3 folder once thats done unplug your flashdrive from your pc go your PS3 plug it into that then go to savedgamedata(ps3) you will see your flashdrive click on that to open it then hit triangle on controller to save roster file to your ps3 and u are all set.