I have an S5, but the steps should be the same:
Open "My Files" (app)>select Images>long press to select desired images>press the 3 dots on the top right>tap move>tap SD card>select folder you'd like to move them to.
When you've navigated to the desired folder, tap "move here" on the top right of your screen. If you don't have the My Files app, any file explorer app should work.