Alewife station parking change?

I'm traveling to Boston this weekend and am planning on parking at Alewife garage. I've checked the MBTA website and the "vehicle exit has been temporarily relocated to the third level". I'm not sure exactly what this means or how I'm going to get back to the street, or why the entrance isn't included! If someone who's been there since the change has taken effect could enlighten me that would be very helpful!