MarkJerling posted a link above.
DCU is what ships with the K-1
See this thread on how to install without a CD.
https://www.pentaxforums.com/forums/55-photography-articles/36984-how-install...installed.html
Basically all you need to do is rename a removable drive as S-SWxxx. I believe it is S-SW140 for v5.5.1. If not run the update install and it will complain and tell you what name it is looking for..
With Windows connect you camera via USB cable or put a card in a card reader. In Windows file explorer right-click on the drive icon for the card and pick "Rename" and change it to S-SW140 or whatever. Then run the update install.