Don't worry about the GPG errors. At least not for now.
The problem is the openbossa repository, it's unavailable. This happens now and then with repositories, the site is temporarily unavailable.

What you have to do is to go into application manager, tools, application catalogue, select/find the openbossa repository and select Details (unless you gave it a recognizable name you may have to look through all of them), then disable it (there's a tickbox). After that update will work.