The update will be sent in two parts one starting this week and a second to complete the process closer to the end of the month. Because of the size of particularly the second upgrade, users are advised to download it via a Wi-Fi network.
The Android 1.5-powered Hero was highly praised when it launched around a year ago, but in the time since it has increasingly been left behind by rivals using newer version of Google's operating system.
An upgrade was first announced back in October, and at the time an HTC statement warned that "because Eclair is a significantly enhanced release, it will require some time to update Sense for this new version of the Android OS".
And those words have certainly proved to be be true, as first a schedule upgrade collapsed in March, then another in April, leaving Hero owners still stranded on Android 1.5.
HTC says the first part of the update will automatically be detected by the Hero's update checks. However, the second will clear all data from the phone, so users should backup before starting.
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