If you're referring to changing your key, this is not possible--you would need to make a new key entirely.
If you're just wanting to change your password, you can do this by navigating to the top right where your username is shown, hover over the down arrow, then select Manage Account.
If you're just wanting to change your password, you can do this by navigating to the top right where your username is shown, hover over the down arrow, then select Manage Account.