Det ändrar du på telefon eller padda.
https://support.apple.com/en-us/HT204264
iCloud Photo Library keeps all of your photos and videos in their original, high-resolution version. You can save space on your device when you turn on Optimize Storage.
On your iPhone, iPad, or iPod touch:
Tap Settings > [your name] > iCloud. If you’re using iOS 10.2 or earlier, tap Settings > iCloud.
Tap Photos.
Choose Optimize [device] Storage.