The update is pretty simple. I have tried it with a MAC and not with Windows yet, but I believe MPLAB IPE has the same process for both.
You'll need a PicKit. I have a PicKit3 and haven't tried it with a PicKit2.
Download MPLab HERE
When downloading, make sure to select MPLab IPE and unselect IDE unless you want the full development suite.
Once you finish the download, open up MPLAB IPE.
Under device, type in 'dsPIC33FJ128GP310A'. That is the MCU used by the Stillson Hammer.
With your PicKit plugged in, you should be able to see it show up under tool. Connect to it.
On the source line, select the Stillson's firmware.
Plug your PicKit into the back of the Stillson as shown:
Click program and it should run through it's little process of programming.
When complete, restart your system and you should see 1.500 firmware on your Stillson: