First of all, you will have to log in. After logging in, where the link 'Log in' normally is, the link 'Settings' will appear. This is the one you will need to click on.
Afterwards, you will need to click on 'Account settings', and enter your new password
in the field 'Password', repeating this same password in the field 'Password
confirmation', and, afterwards, enter the current password and click the 'Update' key.