iPhone 6(+) How to move media to iCloud to free up space

hi

wife has iphone 6 16gb. recently, storage getting full meaning have play around deleting things it. has photos , videos on it, thought easy solution 50gb icloud storage @ £0.79 per month , move photos/videos phone icloud free lot of space phone.

can’t figure out how this!

have bought 50gb icloud storage haven’t been able move photos/videos icloud.
possible, or can copy photos/videos phone icloud, meaning u can’t free space on iphone?!?

have been apple store , have said can done, when tried advised me when got home, didn’t work.

kind person please tell me if possible move photos/videos iphone icloud free storage on iphone.
if possible...could please explain how can (without risking losing photos/videos).

 

in iphone settings

settings>photo>
toggle icloud photo library switch on

below select option
optimize iphone storage

 

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