The forum for your device will have a sticky for the lastest OS. Its all here on Crackberry!
I would suggest only consider upgrading once you are both happy with your device and the upgrade process. The Sticky will provide full details on the upgrade process.
Posted from my CrackBerry at wapforums.crackberry.com
EDIT: Ok I was on wap and couldn't see your device. 4.5.0.77 seems to be available for the 8830 but its a Beta.
i've been running 4.5.0.77 with no problems. Only issue was grabbing the net_rim_bb_medialoader_8830.cod and renaming it to get the default ring tones.
I've read all the posts and still can't get OS 4.5 to work on my 8830. I'm with verizon and went to thier site and can only download 4.2 which I already have. Same thing with the Blackberry site.
I know there's been a lot of talk about this but honestly I'm still confused. I've had smartphones before but this is my first Blackberry so I do have some experience.