You're actually a good deal behind. That's the OTA that updated to froyo (2.2). There have been several OTA updates since. See the first table on this page for a list:
HTC Supersonic/ROMs - XDA-Developers
If your phone is rooted, you should flash the latest radios and a ROM based off the latest OTA (3.70.651.1). You can find instructions in the Rooting for Dummies guide (section 6 under after rooting) in the root section.
If you don't have root, and don't care about it (or might want to do it later), you can just accept the OTA updates. Go to menu->settings->system updates->HTC Software update, and select the option to check now. If the box is checked to check for updates, you should have been prompted if you're that far behind.