RodrigoBS Said:
"System files is taking about 20GB of space: Thanks for the hints. Unfortunately it did not work. I can't restore the iphone, due to the error message that there is not enough memory to restore.
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About Troubleshooting iPhone Storage:
The maximum internal storage capacity never increases, even if you upgraded your iCloud plan. Learn More here: What's the Difference Between Device Storage and iCloud Storage? Apple Support. So, you'll just have to clear space, and then proceed form there.
So, what to do:
Clear Space:
Try clearing internal storage though use of the following:
What Space to Clear:
A. Clear Temporary Internet Files:
Clear your Temporary Internet Files(Cookies & Cache) of Safari:
And...
B. Clean TV and Music Libraries:
Remove all unneeded files from your TV and Music Libraries. Full-Movies take up 2-4GB typically, and a bunch of those would take up a load of storage, ideally. So, if you have any movies that are not needed, then delete them.
And...
C. "Other" being the Culprit:
Use this Link: How to Check the Storage on your iPhone, iPad, and iPod touch - Apple Support. The storage named "Other" is the grey bar. So, to clear that, refer to my User Tip: How to Clear "Other" in your iPhone's Storage - Use Backup - User Tip