Remove Specific Words From Specific Lines?

Here's my problem i am trying to extract data from a forum

Now what i want is to remove a specific word from only a specific line

So here's a example

[quote=randombla13] I am the king of the world bla bla
[img]http//google.com/img.jpg[img]
[quote]This line should not be removed[quote]
[quote]

Now as you can see these are the codes you may have seen in many forums

Now want i want .Net to do is filter the the content in a textbox

And remove only the lines marked with red "[quote=randombla13]" from the first line

And the Extra "[quote]" from the end line

As you can see in the example the content has two "Quotes" so i jest want to remove only one from the first line and last line of the content

And note "[quote=randombla13]" the length after the = is Unknown it maybe of 6 characters or less or more