How to upgrade Apple's mobile phone version because it is too low?

In the settings of Apple's mobile phone, you can use the built-in software update function to upgrade the version. The specific operation steps are as follows:

Tools: iPhone 13, iOS 15. 1, local settings.

1, click General.

In the setup interface of Apple's mobile phone, find the general options and click Enter.

2. Click Software Update.

In the general interface, find the software update option and click it to enter the new interface.

Step 3 open the slider

In the new interface, click Automatic Update, and then open the slider to the right of downloading ios updates.