Please update my iPhone 5

Vik115 wrote:

so how to use it ios 12.4 is required

Buy an iPhone 6 or newer. However, note that many app developers only support the last two iOS versions, maybe a few the last three. In that case you would want an iPhone 6S at the very least. If you buy an iPhone 8 or newer you can upgrade to the latest iOS.

The iPhone 5 is 11 years old. Due to the age of this iPhone, it cannot be upgraded past iOS 10.3.4 If you require a newer iOS version, you will need a newer iPhone