Currently you can upgrade only to the latest available plugin version and downgrade to previously installed plugin. If would be nice if Jenkins allows to offer e.g. combo box where I can choose plugin version I want to upgrade. It's useful when e.g. I want to upgrade some plugin and it's known the in the latest version is some critical bug, which is not present in previous version. This is just for user convenience to can easily do this via Jenkins UI and not have to do it manually by replacing the plugin on the file system level.