Also, check out:
How do I delete an iFormBuilder user?
To delete a user in iFormBuilder, please follow the instructions below. You must be a Company Admin in order to perform this action.
PLEASE NOTE: Deleting a user does not affect data currently on the server. However, please make sure the user has synced his or her devices before deleting the user from the system.
STEP 1. From the admin portal, hover over the Users tab and click Add/Edit Users.
STEP 2. Highlight the user you want to delete and click Delete.
STEP 3. A pop-up will display, asking you to confirm. Click OK.