How to allow users to change their previous response?

Also, is there a way I can have the end user set up an account and password so they can return to their account and change their answer or previous response.

We do not have account features for the users filling out the form but it is possible for them to update their responses at a later date.

Here's how: http://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

If you have further questions about this, please let us know.