If you are a leader of the clan, you can promote a member to co-lead or demote co-lead member to regular member. To do this you need to go to the My Clan tab and tap on the player you want to promote/demote. A bubble with several buttons will appear to promote/demote, tap on button in the middle that says ''Promote'' or ''Demote''.
Here you can also kick a member from your clan. If you kick a player, they will be removed from your clan.
You can also mute a clan member. For this you need to tap on the Mute button. If you mute a player, their messages in the clan chat will not be shown to you.