Open up style.css and replace this:
/*FULL WIDTH PAGE*/
.theron_fullwdth_body .single_post{ width:940px !important;}
.theron_fullwdth_body #content .single_wrap{ width:1000px;}
.theron_fullwdth_body .commentlist{width:100%;}
.theron_fullwdth_body #commentform, .thn_fullwdth_body #newslider{ width:970px;}
.theron_fullwdth_body .comment-form-comment textarea{width: 570px;}
.theron_fullwdth_body .comment-form-comment{width: 600px;}
.theron_fullwdth_body .field_wrap{width: 340px;}
.theron_fullwdth_body .comment-form-author input, .thn_fullwdth_body .comment-form-email input, .thn_fullwdth_body .comment-form-url input{width: 263px;}
.theron_fullwdth_body .org_comment{ width:97%;}
.theron_fullwdth_body .single_post .post img, .thn_fullwdth_body .type-page img, .thn_fullwdth_body .type-attachment img{ max-width:940px; height:auto;}
.theron_fullwdth_body .post_foot{width:1000px;}
.theron_fullwdth_body .share_this{width:960px;}
with this:
/*FULL WIDTH PAGE*/
.theron_fullwdth_body .single_post{ width:90% !important;}
.theron_fullwdth_body #content .single_wrap{ width:100%;}
.theron_fullwdth_body .commentlist{width:100%;}
.theron_fullwdth_body #commentform, .thn_fullwdth_body #newslider{ width:96%;}
.theron_fullwdth_body .comment-form-comment textarea{width: 90%;}
.theron_fullwdth_body .comment-form-comment{width: 50%;}
.theron_fullwdth_body .field_wrap{width: 50%;}
.theron_fullwdth_body .comment-form-author input, .thn_fullwdth_body .comment-form-email input, .thn_fullwdth_body .comment-form-url input{width: 50%;}
.theron_fullwdth_body .org_comment{ width:97%;}
.theron_fullwdth_body .single_post .post img, .thn_fullwdth_body .type-page img, .thn_fullwdth_body .type-attachment img{ max-width:100%; height:auto;}