It can be updated, but it is on iOS 4 or even 3.2. Before iOS 5 you can't install system updates directly on the device.
That means you have to plug it into iTunes on your computer. If you have the latest iTunes it will tell you there is an update available and will download and install.
If the computer you plug it into isn't the one your brother used it will want to erase everything off the device (It can only sync with one computer.) If you don't care you can do this, or if you want to keep everything on their click the button that doesn't erase & sync.
If you don't erase, make sure you right click the device in iTunes and create a backup before updating.