To move photos from your phone memory to a memory card, tap Files > Images. Press and hold the photo you want to move, and tap more_vert > Move to SD card.
To move documents and files, tap Files > Documents & Others. Tap keyboard_arrow_down next to the file name, and tap Move to SD card.
To remove unnecessary files from your phone, tap Files > Clean, and select to remove duplicate or large files, for example.