How to scale footages to HD with 1920×1080 res

When shooting videos in 4K with 3840×2160 resolution using the Panasonic Lumix GH4, is it possible to scale most of the footages to HD with 1920×1080 resolution? If this is possible, how can it be done? Is there a way to do this without making several copies of 4K footages before scaling it to HD?
