How can i change the radius of the fields? For example the modules?

Hi there,
search the div class of the object which you wanne change and then add the "border-radius" css code into the css/custom.css
www.w3schools.com/cssref/css3_pr_border-radius.asp
www.joomlaplates.com/template-customizing

We are committed to help you with any type of support query, however we can't provide extensive help in terms of customizations. In general customizations may look simple but you will require solid knowledge of web technologies and programming skills to do them or hire a professional who can do it for you.

Problem solved.