I want to upgrade my phone software to iOS 15.5
I want to upgrade my phone software to ios15.5with my iPhone
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Assuming you have a compatible device, you can update to iOS 15.6, 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.