Do you see a pink button My account in the top right corner of your screen? That means you are already signed in. Do you see the button Sign in? Then you have to log in first.
When signed in, click the pink button My account in the top right corner of your screen.
Click the black button Change under the header Account details
Change your password.
Submit your current password at Current password.
Choose and submit a new password at New password.
Confirm your password at Re-enter new password.
Click on Change password.
You can now log in to your account with your new password.