Re: Cannot "system upgrade" from 2.0 to 2.0.2.
One, under System Config, you need to copy and paste your Public and Private Access keys from your Magento.com account. On the Magento.com website, these are found under My Account > Connect > Secure Keys. This should resolve the "Sorry, we can't take that action right now" error.
Two, if you installed by zip file (as you should if you are not a developer), the upgrade system is broken for versions before 2.0.2. See 2.0.2 Release Notes for details and how to fix. Alternatively, if you are still testing things from scratch, you can reinstall using the Magento 2.0.2 zip version.