Can I assign/unassign the roles of participants and if so then how?
Yes, you can assign or unassign roles to users provided you have the permission to do so. As always higher role users can edit the roles and permissions for lower roles. The order of roles in Cliq channels is Super Admin, Admin, Moderator and Members. Therefore the super admin can edit roles for all users, admin can edit roles for moderators and members, moderators can remove members.
To assign or unassign roles go to Participants View by clicking on participants count below channel name. Here, hover over the user, click on actions icon that appears and select the role you want to assign or unassign to.
Note: If the creator of a Personal or External channel wants to leave that channel, then they should assign a participant as the super admin.