You can resize partitions in Windows so one way to do it would be to shrink the NTFS partition with the media files from the Windows disk manager, then use the free space in Linux for an ext4 partition, copy the media files, then use GParted in Linux to remove the NTFS position then move and resize the Linux partition.
Of course this is quite convoluted so the safest would be to copy the files to another disk while you wipe the other one and format in Linux, then copy back.