Moving files to the sd card is very simple and can be done right from the phone. First thing you will want to do is open the app drawer by touching the circle with the 6 dots in it at the bottom of the screen and then select Files.
Then choose Device storage and locate the file you want to transfer. Long press (touch and hold) the file. You will see some new options appear at the bottom, touch the one that looks like a box with an arrow in it.
Finally use the drop down arrow towards the top left that says selected and select SD card. Once there find the location you want to move the file to and touch MOVE in the top right.
That file is now on the sd card and no longer taking up space on your phone storage.