There is this function at the top left of the web page which says "Search"
I would suggest using that for your theme question.
You see alot of updates because there are different variations of the Curve. Each model needs a specific software. To the end user these upgrades are usually transparent.. minus a few added options here and there. Only upgrade if your carrier provides you with a link, which you will be able to find on either BlackBerry
or your carriers support website.
Also, For your question, "How do I install an updated OS" You will find the search option also very useful.
The first post of each upgrade thread usually provides some sort of documentation and step by step instructions on how to accomplish this.