The validation on the login page has 2 part to it:
1) Spry Validation, to edit spry validation settings, select the password form element, notice the blue bounding box that surrounds it, click the blue bounding box, this will trigger the spry settings in the Property Inspector and allow you to make changes to the spry validation settings like Max number of characters, min characters, max or min numbers etc.
2) Server Validation. To edit the server validation settings, open the server behaviors panel (Window -> Server Behaviors) and double click the Server Validation server behavior. Select the password validations to change their settings.
for the captcha, in design view, double click the captch place holder image, in the property inspector, there will be an edit button for the captcha to allow you to make changes to the setting.
for the security question. you can delete the security question form element from the page, then edit the server validations behavior and remove the like entry validation for the security question.