URGENT: ICLOUD, windows pc, syncing photos and videos defaulting to c drive

Hi,

I need to find out.

I am syncing my photos to my pc via icloud.

I want to sync photos to my external A hard drive.

Now the issue I'm having is this.

I have synced photos on my windows pc.

On the left when I go to the photos icloud section drive, photos show, when I click the cloud icon the photos download to my computer. Then the blue icloud icon changes to a green tick.

Now, the files are downloaded to my hard drive C(default).

I don't have much hard drive space, around 3 gb left and I don't want to turn off my computer.

I need to delete all these photos from my C hardrrive, the computer itself.

Now what is actually happening here because I want to save all these icloud photos like 50,000 photos to my portable A drive they are saving to C computer drive.

How do I delete photos/videos from my computer that is where are they saving to, which directory/temporary, Cache etc. where? Where do I delete from because it is using up all my space on my computer?

I need urgent technical help!!