I'm using the module Userforms to add forms to my site. But now i'm woundering how can I adjust the look of the
fields, getting the label and field on one line, getting rid of the frame around it and adjust the look of the button so that it's the
samen as all the other buttons on my website.
No, no... Never modify any of the files that are distributed with the module. SilverStripe allows you to override the templates and stylesheets of external modules. Are you familiar with how theming works in SS?