K2 Appit 1.4 was the first version to receive the app catalog-registered version of K2 for SharePoint. If you are upgrading to Appit 1.5 or later, remember that you must first add the new .app file to the app catalog. Then you can upgrade the app to the latest version. If you do not see the indication in SharePoint that there is a new version available, go into the Details page of the K2 Appit for SharePoint app.
Once the app is upgraded, run the Registration Wizard using the Registration Wizard link in the Administration section of the K2 for SharePoint page. If you do not see this link make sure you are browsing the app catalog. For more information see Upgrading K2 for SharePoint to an App Catalog-registered App Version
You do not have to deploy and activate the app to existing sites that have been previously integrated with K2. However, for new site collections and new subsites that must be integrated with K2, you must use the Administration links (Manage App Deployments and Manage App Activations) to deploy and activate the app to those new sites and site collections