Can’t install update of my phone

Without any other information, perhaps these articles will help:

If your iPhone, iPad or iPod touch won’t update - Apple Support

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

If you provide a little more information someone can probably help you. Such as:

• Are you updating by going to Settings/General/Software Update on your phone, or updating using your computer?
• What do you see when you try?
• Any error messages?
• What are they?

Your phone is in Low Power mode, which disables background activity. You need to turn off low power mode. And you also can’t be in Airplane mode, because the phone won’t be able to activate with your carrier.