Is it possible to change the user name in Vtiger CRM?

Yes, you can change your username in Vtiger CRM. The steps vary depending on your role.
For standard users:
Follow these steps to change the username for standard users:

1. Log in to the CRM.
2. Click the User Menu on the top right corner of the CRM screen.
3. Click Settings. The settings page opens. 
4. Look for the User Management section.
5. Select Users. The Users page opens.
6. Hover over the username of the user you want to change. 
7. Click the More icon.
8. Select the Change Username option. The Change Username window opens.
9. Enter or select the following information to change the username:
   1. User Name - Enter the new username. 
   2. Password - Enter the current password to authorize the change.
   3. Confirm Password - Re-enter the current password to confirm.
10. Click Save.
11. After saving, you must verify the new username.
12. Open the user record with the new username.
13. Click the exclamation mark beside the Username field.
14. Click the Click here link in the tooltip.
15. This action will send a verification email to the email address linked to the user account.
16. Open the email and verify the email address. 

For account owners, you cannot directly change your username.
Follow these steps to​​ update the account owner's username:

1. Create a new user and assign admin rights to that user.
2. Log in using the new admin account.
3. Go to your main account and change its username.
4. Reassign admin rights back to your main account.
5. Delete the temporary admin account.