Drive is full , how do i delete some files, do not want to erase whole disk

My WD ‘My Passport’ has become full. I’m struggling to find out how i can remove some files from it to create space. The only support material I can find talks about erasing the whole disk and starting again, which I don’t reaqlly want to do. Can anyone help? Thanks

you open the disc up in windows explorer or mac finder and erase the files and folders you don’t need.

what’s so hard about this?