When you say upgrade, im going to take it as to 'better you character/ship'
In order to do so, your financial funding plays a major role, so running missions from different agents in your range (something your ship can handle; not too challenging) Killing enemies would get you bounty, completing missions and the agents will issue rewards as part of the contract AND, the most important part of all, scavenging. Make sure you get that down first, once you can loot efficiently, you'll be making millions within a couple of hours. Once you have a nice fat wallet, you move on to skill books. Well, while you're making money, you should be buying basic/foundation offensive and ship commanding/upgrading skills aswell. But after you've made enough money, the skill books im now referring too are the more fancy ones.
That would be the main part of 'enhancing' your character.
Note: Whilst training, grab as many learning skills as possible, they further increase training time, enhances player accuracy, charm etc. it's very useful especially when earning rep with agents.
After that, you'd be working with your experience. A major part of the game deals with money and missions etc But in order to do your job correctly while making lots of ISK, your ship comes into consideration. The armament of the ship and its statistics. Again, good ships come with hefty prices so dont rush the missions, do what you can. For every ship you use on a mission, especially when the objectives become harder, you have to decide what you want to arm, consider the enemies and how they would counteract. In the end, your instincts would be utilising the guns you, yourself equipped on the ship, if they ain't right, you're gone. Once you've become a bigshot in the universe, and supposedly you've got a wide variety of ships, make sure you have the guns and upgrades etc to support that.
Note: It would be easier also, considering insurance etc, to belong to a corporation or have a corporation which can effectively mass produce ships. With the money your Corporation earns, the more blueprints/ship foundations you can buy and the more free ships you'll get.
Hope that was useful