how to change the comment section

hi there,

I would like to add 2 more text fields, a drop down menu and a radio button at the comments section. I found a site which describes the changes to be done at the comment form, but this doesn’t seem to work. Could you advise please where I can change the comments section ?

I already added a plugin which gives the option to upload files to the comments section.

The name of the site is Mahala.nl

I am quite new to wordpress. Any help you can provide will be highly appreciated. Thank you very much!

Kind regards,
HLA