Remove them from the space
- Open People in the space.
- Open the person's menu and choose remove. Joyn confirms: Are you sure you want to remove this user? You can always invite them again.
That single step removes them from every group, channel and event in the space. They can no longer see or post anything in it.
You need the Remove members permission. It is off for members by default, so this is usually an admin's job.
If they were the owner
An owner cannot be removed. They have to hand over first: on People, open the new owner's menu and choose Transfer ownership. After that they can leave, or be removed like anyone else.
If they should stay in the space but leave a group
Open the group, go to People, open their menu and remove. The confirmation says You can always add them back. They keep everything else in the space.
Open invitations
If they had an invitation that was never used, or you invited a whole team with one code, check Settings and Invitations and revoke anything that should no longer work.
Group chats
Private chats are separate from spaces. Removing someone from the space does not remove them from group chats they share with your members. Open the chat, go to People and remove them there, or leave the chat and start a new one.
Letting people remove themselves
Anyone can choose Leave space from the space's menu, and Leave group from a group's. A member who leaves on their own can be invited back at any time.