My iPhone 7 Plus storage is 16gb how I can update it

Update it to what? If you are asking if you can add more memory, the answer is no. Once purchased, iPhone memory can never be increased. This is one reason Apple no longer sells any device with only 16GB of memory anymore. In today's world, it's just not enough. You have two options.

1. Delete things you don't need such as App, Photos, Videos, Music, Messages, Email, Files, etc., you don't need or use
2. Or, buy a newer iPhone with more memory

You cannot increase the storage of an iPhone. However, you can optimize iPhone Storage by using iCloud Storage. Save space on your device

Settings > [your name] > iCloud Tap Photos > Choose Optimize [device] Storage Set up and use iCloud Photos - Apple Support

You can buy iCloud Storage. --> Buy more iCloud storage - Apple Support

You can manage your storage --> How to check the storage on your iPhone, iPad, and iPod touch

Manage your Storage --> Manage your photo and video storage - Apple Support

Your photos are always available for both iPhone and iCloud. You delete it on the iPhone it is gone from iCloud and vice-versa. To save space on your iPhone use optimized iPhone storage. Remember, if you delete in one it is deleted everywhere.

Get started with iCloud Photos:

1. Tap Settings > [your name] > iCloud > Photos.

1. Turn on iCloud Photos.

1. Select Optimize iPhone Storage to save space on your device.

With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud. And as long as you have enough space in iCloud, you can store as many photos and videos as you want.

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