Problems with the size of Youtube films

Hi! I have problems with the size of Youtube films when I put up the embed code in posts and pages. I cant adjust the size but instead it will be the full size all the time. See here: http://www.isaynodrugs.org/var-forebyggande-droginformation-pa-youtube/ How can I handle the size of these Youtube films? It works very good on other sites and themes. Pls let me know. Thanks! // Peter :)