How can I upgrade stability for playing special ops?

Stability is under the “Upgrades” section of each weapon. Some weapons will not upgrade to the level needed to enter/complete the Spec Ops section of the particular level you’re on, so be careful to check your weapons max’s Against the mins needed for the missions. If they’re too low and you’ve upgraded your weapon to max stability, you’ll need the next higher weapon to complete the spec ops mission.