As an admin, when connecting to PayPal Donations in Test Mode and the PayPal account is "under review" (in this case a live account), it is not possible to disconnect PayPal using the Disconnect button. When the Disconnect button is pressed, a JavaScript error is thrown (see attached image) and nothing happens.
The workaround is to edit the database. Removing the option_value of give_paypal_commerce_sandbox_account in wp_options will remove the connection so another account can be connected. There will be a warning "Warning, your account is not ready to accept donations.", which doesn't affect anything - but the fix for that is removing the option_value of give_paypal_commerce_sandbox_account_errors in wp_options
After fixing the issue, ensure to use a PayPal Sandbox Business Account to connect.