At some point in the game, you will get a quest called Locked Mementos from Impa at the Kakariko Village. To improve Sheikah Slate, you must complete this task. Here are the consecutive steps:
- Head to Fort Hateno via the road,
- When you get there, turn left a bit, until you reach Hateno Village,
- In the village, go to the Hateno Ancient Tech Lab and talk to Purah and Symin.
You will learn that you can improve Sheikah Slate, but first you have to get the blue flame from an ancient furnace, located in the village. The task is simple - locate the blue flame and carry it to the lab using a torch. To make the task simpler, light all the torches that you will find along the way. When you reach the correct location, use the flame on the furnace to activate the machine. Talk to Purah and you will unlock new options and possibilities of the Sheikah Slate:
- The camera,
- The Hyrule Compendium,
- The Album.
When you upgrade Sheikah Slate, Purah will propose further improvements to your runes. However, it is necessary to provide her with the correct materials. The simplest way to acquire them is to fight the Guardians, which makes the task quite challenging. Upon the delivery of the specified items, the lady will improve one of the runes:
- Sensor+: the Sheikah Sensor can now search through the Hyrule Compendium in search of any item.
- Bomb+: Bombs will be more powerful and will be ready to be used again faster.
- Stasis+: Will allow you to freeze enemies and prevent them from making any movement.