Trustee of Trust

When the Trustee of a Trust brokerage account is changed, does all the paperwork signed by the former Trustee have to be resigned by the present/new Trustee in order for trades, etc to be valid?

What kind of trust is it?

Of more concern, is why was the other trustee replaced, did the trust name a successor trustee, and what is the relationship of the new trustee to the donor?