HVAC airflow trouble in my baltimore city duplex

[Solomon Morris]

I have an HVAC system servicing a 3 level rowhome split into a duplex. There are two separate entrances to the rowhome with one entrance leads upstairs to a 2 floor, 2/1 apartment.  The other goes downstairs into a studio apartment where the actual HVAC is located.  My PM received a request for the HVAC to be looked at by the tenant in the 2/1 due to air not reaching the 3rd floor where his bedrooms are located.  When a service tech went out, he confirmed the unit is operating but air is just not adequately making it's way to the top of the rowhome where the bedrooms are. the main floor is cool but upstairs is a few degrees warmer.  

My PM just sent an email for purposed work by Albrights Mechanical for my approval to install a new control board on the HVAC unit for $467.  I asked to see the work order/invoice for the purposed install, any other notes from the visit and also asked if that install would alleviate the airflow concern, she stated "i'm not sure that is something they can guarantee."

Baltimore city investors, I'm not too familiar with HVAC but will a new control board be the answer?  Although it operates, the HVAC is old, should i consider just biting the bullet and installing a newer model?  Will a newer model push more air to that third floor? 

Looking to get feedback from those who have dealt with this concern or knowledgeable with HVAC systems. Thank you all for your time.

Respectfully,

Solomon