How can I delete a user from Zoho Campaigns and replace with another employee?

How can I delete a user from Zoho Campaigns and replace with another employee?

I did not realise there was a limit of 5 users on Campaigns. I either need to add another user or delete one and replace with another employee who definitely needs access.
 
I seem to be able to deactive but not remove/delete.
 
Please help.