Well there are a few ways. You can check in the phones gallery program and see if it allows for moving them over. Usually it will be one at a time.
You can download and install an app (there are a few) that will help you move them over and manage them. But these apps have drawbacks of wanting permissions etc.
Or you can connect the phone to a computer via USB, move the files over to a folder on the computer, organize them however you want (sub-folders, new names, specific order, etc.,) and then copy them all back over to the SD card rather than to the phone itself.
I say 'copy' rather than move because it is always best to save a copy of your photos, videos, etc., to a computer or cloud account so that you don't lose them should the phone be lost, stolen, die, the files get accidentally deleted, etc.