Change submit button class to follow Site CSS

Hi Guys,

I’m trying to change the “Send” button class to follow the site CSS, i.e. make the form send button look like the rest of my buttons.

When I use firebug to inspect the form, I can do this by changing:

<input class="wpcf7-form-control wpcf7-submit" type="submit" value="Send">

to

<input class="art-button" type="submit" value="Send">

This gives me the desired outcome in firebug, but I can’t find out in which Contact7 .php file I must make the class change?

This is the form if it helps:
http://dotblog.dk/kontakt-dotblog/
It’s in Danish, but should give you an idea of what I’m talking about.

http://wordpress.org/plugins/contact-form-7/