how do You delete all posts of some vBulletin forum user while not deleting his threads?

In my case i use vBulletin module [GlowHost] Spam-O-Matic - Spam Firewall stops forum spam and it allows this. Find some post of bad user, tick the post, scroll the page down and click "Moderation tools" / SPAM-O-Matic...
and there you will be able to either delete all content of the user or untick threads from deleting. One can also ban user instead of deleting.