How do I update the OS on my device?
I have a Cell phone Htc sensation with Android system 2.3.4 i try to check for updates it says that there is no new updates is there any way to update my system to Android 4.0 manually
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This page from HTC's website should help you. This might depend on your location and carrier. So please go through the site.
Another option, if you are ready to void your warranty, you can go for a custom ROM like CyanogenMod.