is it your own blog you are talking about? in that case just undo what you did to put the code there in the first place. find the code where you put them and just remove it.
Delete the plugin if it uses one. Or delete it out of the template in the theme editor under the design tab in your wordpress control panel.
well.. if it is ur blog.. just go inside the template.. look for/search for " src="http://pagead2.googlesyndication.com/pagead/show_ads.js " then crawl up, look for something codes contain like this <script type="text/javascript"><!-- google_ad_client = "xxx"; //--> </script> . ... ... <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> and then remove it from where it starts ( <script......) to the end ( </script) Thats all.. or just replace with new clean theme/templates that no adsense code on it..simple act...