In this article, you will learn how to change the username (namely, the name of the character) in the computer version of Minecraft. This cannot be done in Minecraft PE and console versions of the game because they use an Xbox Live or PlayStation gamertag.
Steps

Step 1. Understand the limitations
You cannot change the username if less than 30 days have passed since the account was created; also, the username can only be changed once every 30 days. Keep in mind that the username must not be the same as the name chosen by another player.
If you change your character's name (in-game), the profile name (on the Minecraft website) will remain the same

Step 2. Go to the Mojang website
Go to https://www.mojang.com/ in your browser.

Step 3. Click on ACCOUNT
This tab is in the upper-right side of the page.

Step 4. Click Log in
It's in the upper-right side of the page.
If you are already logged in, skip this and the next two steps

Step 5. Enter your credentials
Enter your email address and password on the appropriate lines.

Step 6. Click on Log in
It's a green button at the bottom of the page.

Step 7. Find the "Profile Name" section
It is located in the middle of the page.

Step 8. Click Change
This link is located to the right of the current username.

Step 9. Enter a new name for the profile
In the text box at the top of the page, enter a new name.

Step 10. Click Check availability
It's a gray button to the right of the profile name text box. The system will check if this name is taken by another user; if not in use, the message “username is available” will be displayed.
If the username is taken, the message “username is use” will be displayed. In this case, enter a different username and click Check Availability

Step 11. Enter your password
In the Password line at the bottom of the page, enter the password you use to sign in to your Minecraft account.

Step 12. Click on Change name
It's near the bottom of the page. The username will be changed; you will see it when you log into your Minecraft account on your Windows or Mac OS X computer.
- Remember that your username can only be changed once every 30 days.
- The old username will be available for 37 days, meaning you have a week to change the new username to the old one (if needed).
Advice
- If you change your gamertag, it will be noticeable in Minecraft PE and / or the console version of the game. Please be aware that you can only change your gamertag a limited number of times and may have to pay for it.
- Changing your name will not affect your admin or whitelisted user status.