If I remember well with the free version, the member you want to remove has to be in a team you have access to.
Then 2 cases:
- you are already both members of a common team, then ok
- or you need to invite that member “temporarily” to a team you’re member of
Once you are in a same team, you can access to the team’s member list, you select “remove” next to the member’s name you want to remove access, then “remove access”. If you stop now you just remove the member from the team, but at this moment you can select “deprovision” and the member will be removed from the whole organisation.