Connecting your phone to a PC is the best way.
With W10M the File Browser App does this job without needing to plug into USB.
Ah. Two opposing viewpoints. Let's start an argumentative debate. Better not, let's not argue at all.
I haven't done this in a while, but I feel the need to expound on the merits and drawbacks of each method, just for the sake of helping others in the future deciding what to do.
What's easier for someone to do depends on the individual. There are advantages and disadvantages to both methods.
I frequently move photos and downloads from internal memory to SD card. I have much more storage on the SD card, and prefer to keep the long term storage photos there, but I like to save photos to my internal memory because I can take more pictures consecutively without getting the "Saving" message or having to wait. As they build up a bit, I move them over to SD Card.
The "Plug it in to a PC" method is easier because you can use two windows of Explorer in split screen and drag/drop the files from one folder to another quite easily. You can also move multiple folders at once, which is a real advantage. So, easier to browse to what needs moving, easy to move multiple folders, easy drag and drop are the advantages here. However, since each move command is actually a "copy" followed by a "delete", and since the PC is actually issuing the commands through the USB cable, there is slightly more lag to the copying than if you did it from within the File Browser App on the mobile device.
The Mobile device app is easy to use, does the job slightly faster (especially if you have a large number of files), and the "select all" functionality allows you to move all files in a folder with ease. The big drawback is that you can't easily copy multiple folders at the same time. You have to copy the folders individually.
Also consider that not everyone has a PC available, and that will make the File Browser App the better option for those people every time.
I do agree it is easier when connecting to a PC, but it does take time to connect the cable, wait for the PC to detect it, then browse to the locations for moving. If you only are moving items from one folder, like the Camera Roll, it's much faster to just browse using the File Browser to the local Storage Camera roll, select all, and move. Especially since many people will also have to boot up their PC in order to do it, or wait until they are at that PC in order to hook it up.
For me, small moving jobs is just easier on the mobile device without using a PC. However, for big jobs with a lot of different folders, it will be easier using a PC.
-- rhapdog
-- Master of the inordinately long post.