Your recordsets on the update and delete pages should look something like:
$termineedit = new WA_MySQLi_RS("termineedit",$aktuelles,1);
$termineedit->setQuery("SELECT * FROM Termine WHERE ID = ?");
$termineedit->bindParam("i", "".(isset($_GET['ID'])?$_GET['ID']:"") ."", "-1"); //colname
Then you should be linking into this page with something like:
Where the 2 at the end is the record you want to edit or delete.
Let's concentrate on one page at a time. It is hard for me to advise you how to fix three pages at once without it getting confusing.
Do you have a results page? That page is needed to link to the update or delete page and display the right record.