How do I unlock aspects of weapons from the armory? What button do I actually press?

[adult gamer rachael]

How do I upgrade my weapons? All I see is "equip" when I go over to one. I have heaps of stygian blood, unlocked all the weapons and have beat Hades twice. Please help anyone?

[Nibbie]

You interact with the weapon that you are currently holding, as in you swap to it then attempt to 'swap' to it again. Note you have to unlock all the weapons and do a run after that for the feature to unlock, Skelly will say something about your weapons when you unlock the feature.

[RCMidas]

You also cannot unlock new Aspects for all Weapons at once. Each one is revealed over time through conversations with other characters telling you how to do this. I should also point out that to fully upgrade all Weapon Aspects, you will need somewhere in excess of 300 Titan Blood...so you're going to need to do literal hundreds of runs to get enough.

Don't sweat it. Don't try to rush it. You'll get there in due course.

[Alex P]

The action is basically "picking up the weapon twice" - first time it's picked up, the second time you get to choose aspects / unlock them. Hope this helps.

[Almo]

just play the game, eventually someone will tell you a secret about a weapon, than when you go to that weapon aspects it will unlock

[letir]

To start unlocking secret weapons you need:
1. Purchase the Fated List of Minor Prophecies from the House Contractor
2. Reach the final boss (defeating the boss is not required)
3. Invest Titan Blood into 5 separate non-Zagreus aspects
4. Talk to Achilles (with any weapon equipped) until he gives you the waking-phrase (" I see you through the eyes of the crimson phoenix")
5. Equip the Spear at the House and then interact with its placeholder to reveal the Aspect of Guan Yu

3 is most important prereqiusite here, and you need to stumble on 4 over time.

After unlocking spear, you need to get key phrases from different characters to unlock other weapons.

Source: https://hades.gamepedia.com/Hades_Wiki