We’re moving away from bower in v2. Running ionic lib update is running bower update ionic under the hood, so this won’t work with v2.
I would recommend (for now) updating the package.json file to the alpha version you’d like, the latest is currently 2.0.0-alpha.31, and then running npm install. You may want to remove the ionic-framework folder from node_modules prior to doing this, as it can fix some issues.
Note: we found some performance issues with alpha 31 and we are working through them, so it may be better to stay on alpha.30 or below until we get a more stable release out.
There were also some changes to paths in alpha 31, so if you choose to update to alpha.31 you may want to look at the conference app to see what to update in the webpack.config.
If you wanted to develop against the 2.0 branch of ionic, you could clone the repo locally and use npm link to symlink it, but I don’t recommend it as it is not stable. See these notes for more information: https://github.com/driftyco/ionic/tree/2.0/scripts#developing-against-ionic-locally
Sorry if any of this is confusing, we’re still working through it. 