Most Android systems have a file manager. It might be named that or older versions will be My Files. Find that in the Apps list and open it then choose All or any of the other categories.
Tap the settings bars and Select all. Once selected, tap settings again and yuou have the choice to copy or move. Move it fairly safe but I prefer to advise copy. That way, you can then check they've made it to the SdCard and delete the originals.