If I backup my pictures & videos on mycloud, can I delete them off of my pc to free up space without losing them on mycloud?
Yes, you can.
Just realize, once you delete the files from your computer, you no longer have a “backup”, or two or more copies of your data in two or more locations. If you plan on just keeping everything in once place, you will want to work on a backup plan for the data on the MyCloud. Depending on the model of MyCloud you have, you can use the “Safepoint” software or USB backup feature already installed in the MyCloud.