You can purchase upgrades from Studio One 2 to Studio One 3 at the following link: https://shop.presonus.com/products/software/studio-one-prods/Studio-One-3-Digital-Downloads/studio-one-upgradescrossgrade
If you're encountering an error in this process, you'll want to create a support request from your account by following these instructions: http://support.presonus.com/hc/en-us/articles/210050813-How-do-I-create-a-new-Tech-Support-request-by-email-