Um... you can't delete it, because it's already free space. There's nothing to delete.
If you're trying to move the remaining partition to the "top" (technically outside, I think) of the drive, Disk Utility can't do that. A repartition-on-the-fly app probably can, but the only ones I'm aware of are not free. Alternately, back up your files, reformat the drive and reinstall from scratch--this is safer, anyway.
If you want to expand your remaining partition to fill the whole drive, Disk Utility also can't do that. Same answer--non-free apps should be able to.
If you want to just create a partiton to fill that space, Disk Utility probably can, although I've never tried doing that--select the format you want for it and "Apply."
If I've misunderstood the question, apologies.