Please be sure all chkdsk, windows fast boot and hibernation are complete and off before proceeding. If you change the partition for windows and windows has a lock on the drive for one of those purposes you'll be installing two os's, not one.
Resize the windows partition leaving about 10gb for play. Updates and software will eat it pretty quickly. The unallocated space that gives you can be formatted ext4 (not in windows... windows can't read ext4) that will be where you put zorin. Overwrite the windows bootloader partition to have the dual boot experience. Beyond that, you should be good. If you do make a mess, install using the gpt/uefi style of possible (may have to upgrade your bios though). If make sure the bios was completely up to date before trying any of this.