Update

uttam ~ This update cannot be installed because it requires at least 3.64 GB of available storage during installation. You can make more storage available by deleting items in iPhone Storage, or connect your iPhone to a computer to install the update.

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You also need a WiFi signal and can't be using Low Power mode. It also needs to be charged to at least 50%, you are very close to that limit, plug your phone in while performing an update.