i've got mybb 1.2.1 and when i do the version check, it always say "There was a problem communicating with the version server. Please try again in a few minutes."
i try again a day later, a week later and it always says this message.
can i upgrade my forum by other method
The version check is only there to inform your admin's of MyBB updates. It isn't automated process.
Are you currently test this on your localhost (your PC) or do you have MyBB setup on a server on the internet?
MyBB 1.2.8 will rectify this issue with alternative methods to fetching the latest version (think CURL support).
Also Snake is correct. It merely checks the version, it doesn't update it for you. If you want to update check here:
[Wiki: Upgrading] (Broken link, head over to docs.mybb.com instead)
I would recommend in upgrading to the latest version. All 1.2.x themes and mods will still be compatible.