The ultra upgrade can be bought late in the game for a price of 30,000 credits, this is the maximum amount of health you can have in the game, which is 8. To get this upgrade, you have to first complete the mission on Planet Orxon as Ratchet (you will previously do it with Clank to get an info bot). At the end of the mission there will be the Nanotech Vendor, this is where you buy the upgrade. There's two options, the standard one which costs 4,000 bolts (Buy this for the other trophy), and the ultra one which costs 30,000. If you have that much at this point then buy it, but you will most likely just have to save up and buy it on challenge mode or buy it at the very end of the game if you save for it. If you want you can leave here and come back later via the teleporter by your ship to save you a lot of time and effort reaching this area again. Trophy will unlock after buying it.