Keep all files on the PC and sync new ones to the OneDrive servers (to download the folders and files backed up to OneDrive servers and sync new files from the PC to the servers ‘Backup’ must be turned ON and ‘Files On-Demand’ turned OFF): Click on OneDrive cloud icon in notification area then click on Settings ❯ Sync and backup ❯ then first ‘Manage backup’ and see what is backed up before agreeing to it, then ‘Advanced settings’, and turn OFF Files On-Demand (assuming there is enough space on the hard disk to accept all the files)