How to mass delete posts by 1 author

I upgraded to a newer version of wordpress, it wouldnt work correctly with multiple authors, so I restored and went back to the old 2.0.4..

It works fine now, but nor the database went ga ga, and theres a duplicate blog post on almost every post made, but it only shows the title, not the body. ANd it files it under “Webmaster”, not under the origional author.

How can I deleve all of them, and/or delete everything with the username “webmaster”?

There are thousands of these duplicate posts dso doing them all manually is very difficult.