Assign the ids "link1" and "link2" to the two divs which contain your links. Then simply change the innerHTML:-
document.getElementById("link1").innerHTML = '<a href="http://putlocker.com/embed/51536C523E65AC6B" target="blank">Watch Online</a>'
document.getElementById("link2").innerHTML = '<a href="http://vidxden.com/xiif4kxqdpjg" target="blank">Watch Online</a>'
But I do not really understand what you are trying to do - why do you not change the text of the link directly?
Note that the align="center" tag is obsolete and deprecated - use CSS to style the page layout. Likewise The <td> valign attribute is not supported in HTML5.
"That which seems the height of absurdity in one generation often becomes the height of wisdom in the next". - John Stuart Mill.