Please Note, this process will delete all data on the USB drive.
Right click your Start Button and open Disk Management.
Expand the bottom pane so all drives are visible in that pane.
In the bottom pane, right click the partition on that USB and select 'Delete Volume'
When that process completes, the USB should be marked as 'Unallocated Space'.
Right click the 'Unallocated Space' and select 'New - Simple Volume' and accept the defaults, then wait for that process to complete.