changing password by linux

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The answer from anishjp also work, but if you prefer to do it in the graphical environment you could try:

• In upper right corner, in your name, click on it to open the menu.
• Click in your photo, and will show your account detail.
• Click in the password to change it. It will open a new windows to change it.

From a terminal

login first as the user for which you want to change the password. Then type passwd. It will prompt you for the existing password and then for the new password!