Path of Exile

To upgrade a god power you must first have the epilogue unlocked and have the item Divine Vessel (can be stored in fragment stash tab). Hovering over a map in the atlas can tell you if that boss can be used to upgrade a specific power (atlas changes with every league so I will not be listing them). Each major god (there are 4 of them) has three upgrades while each minor god (8 of them) only has one. This means you will need 20 divine vessels for the achievement. Simply use a divine vessel with the map that has the boss you need for the upgrade in the map device, defeat the boss, retrieve the captured soul from the map device, and then talk to Sin. Do note that using a divine vessel will make the boss harder with more damage and life so be careful!