Maybe this will help:
Go to Settings - Mail, Contacts, Calendars - the account. Tap the account, then the email address. You should find "Outgoing Mail Server" somewhere, with SMTP right below it. Tap that, and if necessary, "Primary Server". There, you should find your Outgoing Mail Server, with username and password and "Optional" next to both. Enter your new password there, if you haven't already.
If this doesn't help, remove the account from your iPad, and set it up again. In most cases, this will help solving problems with email accounts.
Hope that helps.