Should I relocate the HVAC unit in my attic?
Necessary? 
No.

More efficient?  Yes.

When the HVAC is centrally located the warmer/cooler air has less overall distance to travel to cover the entire house, as it's radiating out from the center.

If you have noticed that one side of your house is less comfortable than the other, it may be worth the relocation.  If the house is generally comfortable year round already when the system is operating, I would not bother with moving the new one.