Install iOS 12.7.5

In the absence of any relevant information, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

I want to upgrade my iOS (12.5.7) to better version

ostori wrote:

I want to upgrade my iOS (12.5.7) to better version

Your device is not compatible with newer/better versions.