Simply open the app and it will automatically warn you of a new update. From there, just follow the instructions.
If you are eligible for a product upgrade, the 30% discount will be applied on top of the upgrade discount. The discount will be automatically applied during checkout.
The discount is available from 08/01/2020 00:00 PST to 27/01/2020 23:59 PST on all Sound Particles products. (Includes: Sound Particles 2 and Doppler + Air)