How i can change registration name in i phone

Hi Pushkar_saini_kunal,

The following steps address what you're describing specifically, and should provide a solution:

1. "Go to Settings  > General > About > Name.
2. Tap , enter a new name, then tap Done."

You can find these steps along with other information that may be helpful, here: Change the name of your iPhone – Apple Support

If you are referring to setting up your iPhone with a new Apple ID, the steps here are geared towards that:

Set up your iPhone or iPad - Apple Support

Cheers!