You website content is too small, you should use forum w/o sidebars. Or you should increase website wrapper width.
Also you can use simple CSS code. Please add this CSS code in Dashboard > Forums > Settings > Styles > Custom CSS Code textarea or in current active theme's style.css file. Save it and do CTRL+F5 on front-end to load new content of CSS file:

#wpforo #wpforo-wrap .wpfl-1 .cat-stat-topics{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .cat-stat-posts{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .cat-title { width: 69%; }
#wpforo #wpforo-wrap .wpfl-1 .wpforo-forum-info{width: 60%;}
#wpforo #wpforo-wrap .wpfl-1 .wpforo-forum-stat-posts{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .wpforo-forum-stat-topics{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .head-stat-posts{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .head-stat-views{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .head-title{ width: 69%; }
#wpforo #wpforo-wrap .wpfl-1 .wpforo-topic-info{ width: 60%;}
#wpforo #wpforo-wrap .wpfl-1 .wpforo-topic-stat-views{ width: 15%; }
#wpforo #wpforo-wrap .wpfl-1 .wpforo-topic-stat-posts{ width: 15%; }