Using the Direct Console User Interface (DCUI):
Using the ESXi Shell:
Using the ESXi host client:
Login to ESXi host client using root credentials.
Use drop down of the User root@DOMAIN logged in from top right corner and select 'Change password'.
In the prompt, fill in current password, New password and Retype password.
Click on Save / Change Password.
Note:
If the root password is forgotten, refer to Reset ESXi Root Password with Host Profile.