Remove default controls for autogenerated columns in gridview in asp.net

You will have to covert your fields into templated fields. This will allow you to edit the template and alter the controls as you need.

Click the smart tag of the gridview and click "Edit Fields". Then find the field you want to change and click covert to template. Then in the smart tag again, select edit templates. This will give you access to the default textbox and give you the ability to change it.