I don't recommend doing an OS upgrade just because there is a newer version available, especially if you are new to BBs.
Get to know the device first. Learn what it can and cannot do and make sure it fits what you need. You may find that the things works great for you and there is really no need to go to the newer OS. Generally, a minor release fixes a few bugs that may or may not affect your device and how you use it. By reading the threads here, you can also see that new releases can screw up things rather than "fix" them.
As an example, I had a BB 8800 for about 2 years or so. Upgraded from OS 4.1 to 4.2 for some reason. 4.1 wouldn't do something I needed/wanted to do. After that it worked just the way I wanted so there was no need to go to 4.5 when that came out. Nothing was broken, so there was no need to fix it.