新手求助如何读取数据库中这条记录的字符并更新它

刚开始学习php不久，现在要修改一个小源码，求助如何读取数据库test里的表bbs_runtime中字段v 中以下这条记录的字符。
{"app_name":"Xiuno BBS","urlrewrite":0,"timeoffset":"+8","forum_index_pagesize":20,"cookie_keeptime":86400,"site_pv":100000,"site_runlevel":0,"threadlist_hotviews":200,"seo_title":"Xiuno BBS","seo_keywords":"Xiuno BBS","seo_description":"Xiuno BBS","search_type":"title","china_icp":"","app_copyright":"\u00a9 2008-2010 \u79d1\u6280\u6709\u9650\u516c\u53f8","footer_js":"","iptable_on":0,"badword_on":0,"online_hold_time":1800,"onlines":1,"posts":8,"threads":8,"users":2,"todayposts":0,"todayusers":0,"cron_1_next_time":1370225589,"cron_2_next_time":1370275200,"newuid":0,"newusername":"","toptids":false,"forumarr":{"1":"\u5916\u56fd\u597d","2":"\u4e2d\u56fd\u5185"},"forumaccesson":[],"grouparr":{"0":"\u6e38\u5ba2\u7ec4","1":"\u7ba1\u7406\u5458\u7ec4","2":"\u8d85\u7ea7\u7248\u4e3b\u7ec4","4":"\u7248\u4e3b\u7ec4","5":"\u5b9e\u4e60\u7248\u4e3b\u7ec4","6":"\u5f85\u9a8c\u8bc1\u7528\u6237\u7ec4","7":"\u7981\u6b62\u7528\u6237\u7ec4","11":"\u4e00\u7ea7\u7528\u6237\u7ec4","12":"\u4e8c\u7ea7\u7528\u6237\u7ec4","13":"\u4e09\u7ea7\u7528\u6237\u7ec4","14":"\u56db\u7ea7\u7528\u6237\u7ec4","15":"\u4e94\u7ea7\u7528\u6237\u7ec4"}}我想读取"posts":8出来，并更新为"posts":9，即每次+1，请问如何操作，新手不知如何表达，诚恳各位高手指教。