The surest path to upgrade is to make a "parallel" installation: an Helios Eclipse beside the Galileo one you already have.
Regarding your settings, you just need to reference the same workspace.
In your eclipse.ini, indicate where your workspace is, and you will get back all your projects, workspaces and perspectives just as you left them.
Plugins are trickier, and I would recommend:
In your shared dropins path, you will have:
my-eclipse-galileo-plugins
eclipse
features
plugins
and you will copy all extra plugins and features added since the installation of your Eclipse Galileo instance:
/path/to/galileo
eclipse
features
plugins
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