The size of the fields is a layout information. This means that, in order to manage this property of the field, you need to choose the field from the Outline View of the Grid in which you have placed the unit containing the field.
You can find the "Field Layout" property in the Properties View (in the Layout section).
Clicking on the blue button next to the property you can see a dialog filled with configuration parameters (called Layout Parameters). Some of them are related to the field appearence. You need to change:
- the "Input Size" property if you want to manage the HTML "size" attribute
- the "Input Max Length" property if you want to manage the HTML "maxlength" attribute