I cannot delete files of my WD passport

After buying a new mac I have taken copies of what I need from my WD passport and now need to delete them. I do not need to format it as there is still things I need to stay on there.

Do you have it formatted for Mac? If its only formatted to work on windows computers you wont be able to delete or modify files, only copy them from the passport to the Mac. You might need to backup your files and follow the link bellow to format it.

http://wdc.custhelp.com/app/answers/detail/a_id/3865/session/L3RpbWUvMTMzMDM3MDEyMC9zaWQvMmhvaW5NUms%3D

Yes it is formated to Mac but I wish to just delete some video files of, do you think formating and doing another back-up is the best way?