PC Companion won't update my computer past 1.6

A couple years ago, I picked up an Xperia X10i secondhand. The phone itself has been working great; no problems whatsoever. It's a real workhorse. I unlocked it almost instantly, and followed some steps I Googled way back when to open it up completely. I can't quite remember what it was, but it was supposed to root the phone. I don't think I managed to actually root it, but it's been working fine, regardless. Lately, I've been wanting to update the firmware on it. Every time I use the Sony Ericsson PC Companion or Update Service, though, to try to update the firmware, it just tells me I have the latest version. How can I go about updating this to 2.1 or higher? Are there steps a technically-savvy, but Android newbie could follow to update the firmware? I'm willing to blow it all away if I have to, although I'd really prefer to not have to do that.