The User Registration Solution pack works with client and server side validations. If you would like to alter the validations you could do so with the spry validations and using CSS Form Builder or Validation Toolkit.
If you want to remove a particular field on the form you must also remove the validation for that field. Before you delete it look at the blue colored tab around it to identify what spry is applied to it, then go to the bottom of the page and look for that spry. You must delete the spry validation as well as the server side validation that appears at the top of the page.
If you post back with some more details about what specifically you wanting to change and what field to delete I can give you some more detailed steps to take.
