In most cases you can simply click the database name in phpmyadmin to browse different tables - find mdl_user table and click browse button - usually main admin is the second user in that table, when you find your user account click edit button, enter your new password to the password field and on the left side of password field select MD5 from the dropdown list - GO...
You can also use commands explained in other posts, copy some known MD5 password etc - see for example http://moodle.org/mod/forum/discuss.php?d=137889#p602607