I want to update to iOS 15.7.8

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. 

philomina273 wrote:

I want to update my iPhone

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. 

philomina273 Said:

"I want to update to iOS 15.7.8: I want to update my phone"

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Update Using a Computer:

Have a Computer Handy? If so, try using a computer to update. Go here: Update your iPhone Using a Computer - User Tip

philomina273 wrote:

Not helpful

Then, this would be a perfect time for you to provide details as to what happens when you attempt to update your device.

Want to update my phone

Want to update my phone

Then follow the instructions that have already been posted.