If I update my LR 3.3 to 3.6 will I lose anything? Last time I did an upgrade I lost all changes and development..
Going from LR3.3 to 3.6 should be pretty straightforward. Simply download and install the update and start Lightroom in the normal way.....the update doesn't change anything relating to your existsing catalog or settings, so it should be transparent to you.
That's not normal, Giorgia - as Jim suggests, a "point release" upgrade (like 3.3 - 3.6) should be essentially invisible to the user.
But the risk of a problem is enough to motivate many of us to ensure we've got pretty robust catalogue back-up arrangements.