Which email account? (Your primary, Google email or another one?)
You *should* be able to simply go into the settings on the phone, then Accounts, then Google if it's the Google account that you changed. You can reset the password and sync settings there.
If it's another email account, then you would change the password in whatever email app you are using to access that email.
If you need further direction, post back with more details as to what type of email account and what app you are using to access the email.
