How do I backup my files when my laptop is stuck on the automatic system repair loop?

I restarted my computer the other day in an attempt to sort out a wifi problem but when the laptop started back it it was stuck in the automatic system repair loop. I want to install a clean windows 10 but to get my documents on a USB stick first. How do it do this?
(I have Windows 10 and a Lenovo y50)
It won't let me do an in-place refresh.

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