How can I update my ios

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

An iPhone 5s or iPhone 6 isn't capable of 13 or above; they require at least 2GB of RAM. If you're trying to install 12.5.7, describe what happens.

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