How do I search and replace the contents of multiple WordPress posts all at once?

Ok I have over 500 posts on my website (using wordpress). I trying to replace the < !–More–> tag in multiple posts to single line by itself.
Example

This:

Start of post.......

< !---more--> ...post continues...

To:

Start of post.........

< !---more-->

...post continues...

It would be great if there is no spacing between lines. Thanks in advance..