http://amzn.com/kindlesoftwareupdates/keyboard
The latest version is still 3.4.2 which was the March update.
You can download and install the update via USB, it is quite easy.
Thousands or millions of people have done it already

so you should be fine -- it is fairly bulletproof.
...
Do you really need the update, you ask? Well, you tell me -- do you ever connect the Kindle to Wifi/3G and buy or download books from the Kindle Store? If so, you will need the update...