Synchronize only selected folders in PC

I have a MyCloudEX2Ultra. I use GoodSync to synchronize between everything in Document folder of the my PC and MyCloudEX2Ultra. I will also backup MyCloudEX2Ultra to an external hard drive.
Now here is what I would like to do. As the hard drive storage of my PC is being used up, I want to delete all my photos and videos in the PC, which are all synchronized into the MyCloudEX2Ultra and the external hard drive. But if I do delete anything in my PC, the next time I use GoodSync to synchronize my PC and MyCloudEX2Ultra, it will erase all photos and videos from MyCloudEX2Ultra, as such files are no longer in my PC. So the only copy of these photos and videos is in the external hard drive only.
Is there a way to keep the photos and videos in the MyCloudEX2Ultra, while I delete all of them in the PC?
Thanks for advice.

@twsahdee
Try your sub-forum.
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