How to update my iPhone to ios15

You've been given the answer, and it even shows in your screenshot. You don't have enough storage space to perform the update. And if you're trying to update wirelessly, you need to be connected to WiFi as well.

Here are some helpful articles that can guide you on how to free up storage space on your phone.

How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

 How to check the storage on your iPhone and iPad - Apple Support

Manage your photo and video storage - Apple Support

 Manage your photo and video storage - Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

 Clear Other storage on your iPhone or iPad - Apple Support

Go to Settings/General/About and note the iPhone Model Name, then check its version compatibility from this list:

• iPhone 8 or newer, including SE 2nd and 3rd editions, you can update to 16.3
• Any iPhone series 6S and 7, and any model SE: You can update to 15.7.3
• iPhone 5S or 6: You cannot update to iOS 13 or higher; you can update only to iOS 12.5.7
• iPhone 5: You can update only to 10.3.4
• iPhone 5C: You can update only to 10.3.3
• iPhone 4S: You can update only to 9.3.6
• iPhone 4: You can update only to 7.1.2

After you verify the version you can update to, To update over the air from the phone all of these requirements must be met:

• You need at least 10 GB of free storage for iOS 16 or 6 GB for iOS 15 or lower; more is better
• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is an iPhone that supports cellular 5G (12, 13, 14 or SE 3rd edition) and has a 5G network connection
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN, and it may be necessary to delete any VPN apps and VPN profiles
• The phone cannot be in Airplane mode and must have a cellular data connection
• You cannot still have a beta version installed on the phone
• You cannot have a previous version that was downloaded, but not installed - go to Settings/General/iPhone Storage to look; if you find an iOS installer, delete it

If you can't meet all of them you can still update using your computer.

Your storage is full. Try to delete something

You need to free up space or update using a computer.

Yes