Hi,

If you need to remove an existing field from the view, you can just activate the debug mode and open corresponding form and then click the debugger button on top right of screen near logged in user name. From it click Edit View: Form, then you can see the code of the form, from there you can remove the Field. 

But the above is not recommended and permanent solution, always it is good to do it from the code by creating a custom module. 

To add new field from UI without code, see this:  Add custom field in odoo without code

To make changes inside the form from code, you can do it by inheriting the form, see this example:  How To Inherit And Add Field to Existing Views In Odoo

Thanks