On Macs you have at least two ways to "install" Windows:
- Installing Windows to a newly created separate partition with Boot Camp Assistant.
- Installing Windows using a type-2 hypervisor like Parallels (or VMware Fusion, VirtualBox etc)
In the first case Windows is directly installed to your disk and interacts with your Mac hardware. In the second case Windows is installed to a disk image residing on your Macintosh volume and interacts with virtual hardware entities provided by the hypervisor. The partition layout of your disk isn't effected then.
One way to detect which kind of Windows installation is present is opening /Applications/Utilities/Disk Utility and checking if you have a second partition usually called BOOTCAMP after your Macintosh HD volume.
If such partition is present you have the first type of Windows installation. To delete it open Boot Camp Assistant and remove Windows.
If no such partition is present you probably have the second type of Windows installation. To remove Windows open Parallels and remove the virtual machine Windows (or whatever it is called).