Software Update

Hello~ It is an older iPhone and much has changed and it is just outdated. In order to run higher versions of iOS that many things require now you need a newer device. Go to upper black line and click on iPhone. If you may consider a second hand device please take a moment to read these:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

Yes I am sure, a 6 or older phone cannot be updated beyond iOS 12.5.5

Settings > General > Software Update.

Update iOS on iPhone – Apple Support (UK)

You should be able to update to 12.5.5.

You can try updating using your computer.

Update using your computer -

https://support.apple.com/guide/iphone/update-ios-iph3e504502/ios

What model is your phone? If it's a 6 or older there are no more updates.

Hello ~ What model iPhone and current version of iOS. You iPhone may not be able to be updated further.

~Katana-San~

What do you mean? It came out in 2014. It got an excellent run of software updates…

It doesn’t have enough RAM to run anything newer. Nothing unreasonable about that.

Ask a friend who has a computer if you can use theirs or go to an Apple store and use one of their computers.