The game will throw an error stating: "This save data belongs to another user."
Insert a USB flash drive formatted to into one of the PS3 USB ports. (The PS3 cannot read NTFS or exFAT formats). On the XMB, navigate to Game > Saved Data Utility (PS3™) . Scroll until you find the Gran Turismo 6 save file. gran turismo 6 ps3 save data