The Drive shows as Partitioned and the space is FREE. You need to select the FREE space and go to the toolbar and press Delete, do the same for any other partitions on the drive. Then the drive should be all Unallocated Space then you can go to the Toolbar and create a New Partition. Be sure to press Save All on the toolbar to keep changes.
If you still have a problem, you can select the FREE space and choose to Erase FREE space. Add Unallocated Space to Partition without Data Loss - DiskGenius
Delete is grayed out.