To lower the resolution of your 4K TV, you can access the Settings on your TV using your remote. Within the Settings menu, look for the Resolution or Output Resolution option and select the resolution you want from the list. Keep in mind that the resolution on your TV denotes how many pixels are used to create the images you see, and the more pixels used, the clearer the picture. However, you may not be able to lower the resolution all the way to 720p or 1080p to match lower-resolution content.
When presenting lower-resolution material on a 4K TV, the TV has to perform a process called upscaling. This process increases the pixel count of a lower-resolution image, allowing a picture meant for a screen with fewer pixels to fit a screen with many more. While some people may prefer the upscaled picture on a 4K TV to the native 1080p picture on a regular HD TV, others may not notice a difference. Ultimately, the quality of the upscaled picture will depend on the specific TV model and the quality of the original content.