I downloaded and installed the latest version of Confluence (v4.3.2), but for some reason the version of UPM installed is rather old (v2.0.6) and likely causing issues with installing / upgrading other plugins. I've tried upgrading to the latest UPM (v2.7.10) as well as the nearest version upgrade (v2.1) with no success. I've also tried deleting the contents of the folders mentioned in a comment on a similar question (https://answers.atlassian.com/questions/89470/cannot-upgrade-the-universal-plugin-manager) and restarted Confluence, to no avail.
So, with a fresh install of Confluence using the express install feature and the included database for testing, I'm unable to upgrade the bundled, out-dated UPM. As of yet, I've been unable to turn up any solutions sifting through documentation and Google results. Has anyone come up with a solution to this?