Well the upgrade I was thinking was letting Chung learn how to use the Disfrozen Portal to a greater extent, as well as giving him a gun that would basically be the same as the Deadly Chaser's Silver Shooters (though Chung would only have one Silver Shooter similar to how the Shooting Guardian [Chung's job class before the Deadly Chaser.])
In the Shooting Guardian (which advances to Deadly Chaser) the Silver Shooter(s) are described as:
"While travelling, Chung realises the shortcomings of the Destroyer's slow speed and how open he is to attacks while he himself attacks. As a result, he lightens his cannon and manufactures a second weapon to cover himself should he be open to attacks.
This weapon is called the "Silver Shooter". The Silver Shooter is enchanted with magic and can shoot through any target. As a result, the openings that the Destroyers offer when Chung attacks, makes the Silver Shooter a perfect complement to battle enemies with speed."The Silver Shooter:

Note that in the sequel Chung won't get this upgrade until AFTER they encounter Ran (the Elsword) and they defeated him. Chung would realize that his Destroyer wouldn't be able to handle any situation, hence why he was unable to defend himself against a fast opponent like (Elsword) Ran. Thus he begins developing a new weapon that he was given blueprints for by Echo the alchemist.