To remove a member from a forum:
navigate to the Members tab of the forum
click the edit icon next to the member you want to remove
read the warning and check the I understand checkbox if you wish to proceed
click the Remove button
Important: Consequences of removing a forum member
When you remove a forum member, that person will be removed as an "in full" attendee of all upcoming meetings of that forum - however they will not be removed as attendees of any meeting items where they were specified as a Presenter or Attendee of that item.
Worth knowing: Removed members are still available
Removing a member from a forum does not remove them as a person in the company - so they remain available to be added to other forums or meeting items as required.