In studio there is an account menu icon option "Manage Apps" that allows you to disable app and then delete it. You have to go to Apps Market>Purchases and download the app again then go to Downloads and install again.
That is a good question. If an app/mod get corrupted it looks as if the only way for the average site admin is to disable and then delete it. Past experience resulted in all additional data lost and fresh install creates new tables. In the several cases the error has always been a SQL error and presume associated tables were corrupted. Unless you or someone else has good sql skills to try to correct the errors or able to import the tables in question from a previous sql backup, re-install is the other option.