Q: Deleting iCloud items from MacBook

Hello,

My iPhone 6 broke and I'm gonna hold out til the iPhone 7 before getting a new phone. In the meanwhile I've got an 8GB iPhone 4S. I'd like to synch the 4S, but there is not enough space because my previous phone had 32GB. My question is how to delete some of the data on the iCloud (or iTunes) backup so that I can sync the 4S?

Please bear in mind I can't access my iCloud settings from a phone.

Here's what I've tried so far:

In System Preferences> iCloud I've unchecked all the apps I don't want syched but this has not changed the size of the storage used.

In  System Preferences> iCloud> Manage... I've tried to delete files but the warning message comes up 'All "program" documents will be deleted immediately from iCloud and all of your devices. You cannot undo this action.' I don't want the files deleted from all my devices, I'd like them to stay my computer but not iCloud.

Finder> iCloud Drive is empty.

Accessing my phone backup via iTunes doesn't seem like an option as the device doesn't come up without plugging it in.

(The apps on my old phone can be accessed. I suppose if I deleted them that might reduce the size of the backup but I'd like to keep them on iTunes if possible for iPhone 7.) 

Any ideas gratefully received: I'm stumped.

Rachel