Need help freeing space to update (can we reset native app data?)

Hi there,

I have a Lumia 640 with only 8 Go of storage and I'm on build 10.0.15063.540 but can't upgrade because it tells me I need more free space (I believe that's the FCU?).

I've moved all apps I can to the SD card. Same thing for the photo. I have 625Mo available but apparently still not enough.

The problem is that System takes 4.46Go (I can't free up anything there), and apps take 2Go but none of them can actually be moved to the SD card (Edge, Maps, Mail, Film & Video, Groove, One Note, Skype, WhatsApp, XBox, etc.)

I could free up space if I were able to remove native app I don't use (XBox) or reset app data for other native apps (74Mb for Edge, 20Mb for Film & Tv, etc.), but it's apparently not possible.

What are my options? Thanks in advance for anyone helping :)

[edit: I hope it's appropriate for this subreddit, I didn't see any rules restricting it, but there may be a better place for asking help]