I assume you mean data in the
Saved Data Utility folder, because data in the
Game Data Utility folder is automatically shared by all users, and thus there would be no need to transfer it from one user to another.
To copy data from the Saved Data Utility folder simply sign on as the user you want to copy the data from. Go to that folder, and highlight the file you want to copy. Press the
triangle button to show the option menu for that file. Select copy, and then pick where you want to copy it to. You can copy it to any external HD or memory card, as well as any other *user.
*As long as they don't already have a file using the same name. Some games allow multiple game save files, and so as long as the one being copied doesn't use the same file name, then you can copy it over without having to erase the previous file.