Need Help With UPDATE MySQL

So I have a MySQL wordpress database with several thousand posts in it and I need to update a majority of the posts and take out part of it

ok heres what I got so far, and its just the basic syntax since I have no clue where to go next
UPDATE wp_posts
SET post_content = ""
WHERE post_content = "";

but here is an example of what I would like to do

"...</object>
[then sum more text thats constant throught out the posts]"

... = code thats different in every post
and id like to go though and delete everything after the "</object>"

 

Use SUBSTRING_INDEX() and other string functions to accomplish this.