This happens automatically. Remember the best effect is placing a 4K movie in the unit. The next best thing is the unit upscaling a 1080p Blu-Ray to 4K.
A DVD is very low in resolution. So even though it will upscale it. It can only do so much. The data isn't there for very good quality. The unit is always outputing at 4K.
Just make sure your T.V. and Player have settings for the size of the screen you have. This means that if it is a widescreen picture it might have black space above and below the movie. Don't stretch the movie to fill the whole screen if it isn't formatted like that. The picture will look as good as it can.