Open ''Tools'' -> ''Options'' or, if that option isn't there, ''Edit'' -> ''Preferences'' and select ''Security'' from the resulting window. Click ''Saved Passwords'', which will open a dialog box with all the sites you have passwords saved on. Click the site your password changed on, and choose Remove. The next time you go to that site and input your password, you'll be asked if you want to save your password. Press ''Yes'' and it'll save your new password.