THIS IS ONLY FOR THE PRL...I can't remember how to do the PRI at the moment
I know on my Mogul, the process was as follows:
1. Get your SPC/MSL code by running getspc (there's one for our TP's in the default forum, I think it's entitled "BAF MSL grabber" or something with some other words in there
2. Download the newest .pri, however you can find it. There used to be a website out there that hosted these for different HTC devices, that's how I used to do it for the Mogul.
3. Once you ahve that, you would normally go into ppst.exe located in the windows folder. We don't have that, but I do see an EPST.exe in the TP. Launch that, and then there should be a section where it lists your current PRI version. If you edit that, it should ask you if you want to update it, and then you should be able to browse for the file. Once you're done, your phone will reboot.
I'm sorry, I'm having to do this by memory, and I just installed the slide to answer from the HD, which has disabled my ability to get into EPST.
If this doesn't work, I'll hard reset later and re-word my process above to match what everything says exactly.
****EDIT****
Since I hate not being thorough, I went ahead and hard reset anyway, my phone is currently booting...I'll know if this will work in about 5 minutes.
AND I think my process is for the PRL not PRI....found that page I was talking about, here -->
http://corolada.com/prl/
I KNOW I've updated the PRI too though for my mogul. wonder if it's not the same process. I'll think on it for a while