braindrain's post here and maria_gorbatova's here, I Can I remove or ban a member of my community?
Yes, providing you are the community maintainer.
A maintainer can remove a member by simply removing that member from the community account's friends list. If need be, the maintainer can log in and then remove or ban a user through the admin console ( http://www.livejournal.com/admin/console ), although that will only ban the user's comments. In a closed community, a member may be removed by using the admin console commands listed below.
To remove membership and posting access to a community, log in as the maintainer and use the following command:
community <communityname> remove <user>
To remove posting access to a restricted access community, log in as the maintainer and use the following command:
shared <communityname> remove <user>
To ban a user from your community, log in as the maintainer and use the following command:
ban_set <user> "from" <communityname>
Be aware that at this time, the ban_set command described only prevents the person from commenting in a community; if he is a member in an open community, for example, he will still be able to post.
Note: When entering these commands, do not use < >. These are simply for reference purposes. So, to remove user
gooner from 
lj_userdoc the command would be:community lj_userdoc remove gooner