When a file is deleted, the space used on the disk is not reclaimed until the file is truly erased. The trash (recycle bin on Windows) is actually a hidden folder located in each hard drive. To completely delete the file, another step must be performed.
Files, when deleted, are sent to the "Trash". To remove the file and reclaim the space, empty the trash can.
Right click or press command and click on the Trash can icon and choose the option "Empty Trash".
If that does not correct the free space reporting, then eject the drive by dragging it to the trash can, unplug the drive for 30 seconds then reconnect it.
If the drive still doesn't correctly reflect the free space then run First AID on the drive.
If the drive has been formatted HFS+ or APFS some files may not be visiable to all users. Log in as any other users on the Mac to see if large files may be taking up space.
Files are sent to the "Recycle Bin" when they are deleted from a Windows machine. To empty this folder and reclaim the space, right-click its icon, and left-click "Empty Recycle Bin" on the menu that appears.
If that does not correct the free space reporting, then eject the drive, unplug the drive for 30 seconds then reconnect it.
If the drive is formated NTFS, some files may be hidden from the current user. If your system has multple users, log in as the other users to see if any protected large files exist.