Go here:
https://www.blackberry.com/Downloads/en ... 2F9F00E7D4Select "Blackberry Pearl 8100 smart phone"
You want:
BlackBerry Handheld Software v4.5.0.152 (Multilanguage)
It should come with instructions for upgrading, but basically just make sure you've backed up your device, install that, then connect to the BB desktop manager. It'll notice you have updated software and walk you through it.
Hope this helps (you'll see a big difference in 4.5
)
-Marcus