You can change the author of posts, but you'll have to do it witha mysql query. Do you have access to phpmyadmin to control your mysql database? If so, then give me the user id of the author you want to delete and the id of the author you want to assign the posts to and the version of b2evolution that you're using, and I'll give you the query to paste into phpmyadmin.

old user: ID 6

new user: ID 7

thaks twisters

Try this code in phpmyadmin:

UPDATE `evo_posts` SET `post_author` = '7' WHERE `post_author` =6;