Custodians can be removed by sponsors, from their portals, as long as the Custodian in question has no accounts or payments attached. If there is data attached to the Custodian, removal would have to be done by escalating to the product support team.

STEP 1. Navigate to the Accounts section:

STEP 2. Click on the Custodians tab and select the Custodian you'd like removed:

STEP 3. Click the 3 vertical ellipses then select "Delete Custodian":