Thank you for your reply.
I use Windows 10, and I have an editor program called MovAvi in which I was able to save a "snapshot" in the size 1920 x 1080 px which is the same size I can extract if a pause the video in for example VLC player and take a screenshot.
Do you know if 1920 x 1080 px is the largest size I can extract from a 4K video or can I extract a larger size somehow?