Need help upgrading theme….

I’m a new wordpress user, so learning the basics.

I am using the INove 1.1.4 theme… and have a message in my theme editor saying:

There is a new version available. View version 1.2.3 Details automatic upgrade unavailable for this theme.

So here’s my question. How do I upgrade to the new version (assuming i should).
And will all the contents and layout of my theme (I’ve populated a lot of specific stuff in the sidebar for example) be lost if I upgrade?

And if it isn’t automatic upgrade… what is the process by which you do a manual upgrade?

Basic question – but if someone can answer or point me to a link that explains what to watch for when upgrading, I’d appreciate it!

Thanks!