What steps are involved when replacing control board on Carrier unit?
It was pretty easy.  

First and foremost I killed the power to the unit. I turned off the power to the unit from the breaker box and then pulled the master fuse near the outside unit. 

After that it was extremely simple. I took a picture of the current control board and all the wire placements so that I could hook them all up the same way.  I then unplugged all the cables from the board, removed the screws, lifted it out, grabbed the new board, lowered it in, screwed it back in, put all the cables back on, replaced the fuse, and turned the power back on at the breaker box.  

Once I turned the heat on from the thermostat it took a few minutes for the system to wake up but then it was fine. My heat pump runs like a champ again. 

The HVAC guy was going to charge me $425 to do this job (that included the new board).  I instead ordered the replacement board myself from repairclinic.com for about $110.  The whole job took me less than 15 minutes.  Saved $300.