The Evil Within

In order to upgrade items in The Evil Within, you must acquire an item called Green Gel. Green Gel is scattered in various locations around each chapter, dropped from some enemies, or obtained while opening lockers in the safe room. When you have enough Green Gel to purchase an upgrade, you can go to the restraint chair in the caged room just past the nurse and her save game chart. Sit in the chair to access and view your purchasable upgrades for each category: Attributes, Weapons, Stock, and Bolts. Note that Bolts is not required for any of the trophies and should not be purchased if you only want to get the trophies out of the way. However, upgrading Bolts alongside the other upgrades can definitely help in your New Game+ run for The Quick and the Dead.

Green Gel Jars as they appear in the environment.


Green Gel as it appears when it's dropped from an enemy.
The chart I provided below shows how much Green Gel is required for each upgrade needed for this trophy. The trophy will unlock when you have purchased the final required upgrade.

Farming Green Gel

In order to earn all of the upgrade trophies, without the exploit mentioned in Unstoppable Arsenal, you will need a total of 952,300 Green Gel. There are a few methods you can use in order to make this a little faster than playing through the game two times.

The first method you can use is to replay Chapter 3: Claws of the Horde via Chapter Select*, quickly killing the Sadist on Casual difficulty for a quick and painless 10,000 Green Gel. This method takes about 5-10 minutes depending on skill.

Additional Note* (New Game+ Only) - After killing the Sadist, a crow will spawn in the window of the small room at the top of the barn. Killing this crow activates a short cutscene that spawns in five more crows. Killing these crows within a time limit of about two minutes total will give you a reward of 100,000 experience in New Game+. Finish the level to save your progress and reload Chapter 3: Claws of the Horde with your new saved game to farm this method. Using this method, you can max out all of Sebastian's upgrades in under an hour. (PS3/4 Video Incoming)
The second method is to replay Chapter 15: An Evil Within via Chapter Select*. While this method takes a little longer, you kill a Sadist as well as 2 Keepers for a total of 30,000 Green Gel on top of any other pick ups you get during the mission. Assuming you're skipping cutscenes and can make it through without dying, this is a 13-15 minute run.

Of these two methods, I went with the Chapter 3: Claws of the Horde method because there is less story to skip and it felt faster to me. 10,000 is the minimum amount you can get with that method just for killing the the Sadist. There is also a large Green Gel container in the top of the Barn as well as another one in the watchtower that contains the Flash Agony Bolt. This will bring you to 14,000 Green Gel in about 7 minutes the more comfortable you get with the mission.

*Chapter Select is unlocked by beating the game for the first time. While in the main menu, you click on New Game+ and pick any save you want. You're essentially picking which Sebastian you would like to use in New Game+. After you pick a save, you can pick any chapter you wish to start on.