1. Click Management
  2. Click User Defined Fields
  3. Click the Category where you stored this field
  4. Click the name of the User Defined Field
  5. Click Step 3, Field Attributes
  6. Unmark the checkbox that says "Would you like this field to be required?"
  7. Click Save and Finish
To make a User Defined Field required on your DIY Form, please see How to make a field required on a DIY Form.