Hw to update my IOS 12.5.5

Is your device compatible to update to the new version? See the article(s) below. 

IOS 15 and iPadOS 15 Compatible Devices.  *

iOS 14 and iPadOS 14 Compatible Devices.  *

iOS 13 and iPadOS are compatible with these devices - Apple Support.  *

See the articles below.

Update your iOS device.  -

Get help with over-the-air iOS updates  -

Update – Can’t or can’t restore   -

Have you tried using iTunes on a computer or Finder if running Catalina or later to do the update?

Update software on iOS devices in iTunes on Mac. -

Phone, iPad, or iPod touch - Update with Finder.  *

iPhone, iPad, or iPod touch - Update with iTunes.  *

If you see an error when you update or restore your iPhone, iPad, or iPod    *

Updating iOS: common issues and solutions.  -

ASC YouTube for  how to update your iPhone, iPad, or iPod touch to the latest version of iOS or iPadOS —wirelessly or using your computer.

See this Apple article: Change your Apple ID

Change your Apple ID - Apple Support (SG)