First, back-up the Bootcamp instance using a tool like WinClone. If you're a heavy Bootcamp Windows user, it's well worth the money. Put that clone on an external disk as you're probably pretty low. Remember to shutdown the Windows instance and Parallels before you do the clone. With this, the worst case is that you can delete and recreate the Bootcamp partition and restore the Winclone clone to it.
Next, boot into Windows via Bootcamp. Download and install MiniTool Partition Wizard Free Edition and launch.
Select "Move/Resize Partition," set the new size you want. Select the "Using Enhanced Data Protecting Mode" checkbox and click OK.
Once complete, boot back into macOS and use Disk Utility to recapture the old NTFS space you just freed up.
Resizing partitions can be harrowing, but I did this process once a couple of years ago before I switched to VMWare and it worked fine. Google "reducing Bootcamp partition" for a more detailed step by step guide. When in doubt, back up!