I resently played my first game of legion and had a question about unit numbers I played impearl side and looking at the card the unit is a unit of four which can then be upgraded to a fifth which would put the unit at a total of 5 minis now there is the upgrade that allows you to have either the heavy guy for rocket guy now my question is out of those 5 mini do I upgrade one of the five to either heavy or rocket or do I add either one of those to the unit of five to make them a unit of six?

You add an extra trooper with heavy weapon to the unit. You can add him to either small unit, making it 4 regular troopers and fifth with either DLT19 or HH12, or you can add him to a unit that you also equipped with extra stormtrooper, making that unit 5 regular and 1 heavy troopers.