There are 3 types of File channels: individual client channels, company channels, and group channels.
For differences between the types of channels, please review this article here.
Depending on the type of the File channel, there are different ways to edit members listed below:
Individual client File channels
Individual client File channels cannot be edited or deleted. If you wish to delete the File channel for an individual client, the client must be deleted. (check if true for default company portals)
For instructions on how to delete a client, please see this article.
Company File channels
Company File channels are visible to all members of a company. If you wish to edit the members of a company, you will need to do so from the Clients page. Adding or removing a company from a client will add or remove the client from any company channels.
To assign a company to a client, please see this article.
To remove a company assignment from a client, please see this article.
Group File channels
You can create a group File channel if you wish to share files with a subset of clients within a company. Group channels are currently only supported for clients assigned to the same company.
For instructions on how to create a group File channel, please see this article.
To edit members of a group File channel, click the ellipsis next to the +New button in the top-right of the File channel. Select Edit members, and add or remove members using the checkboxes in the dropdown: