Assuming you are using a relatively modern Windows system zip support is built into Windows Explorer. Here are some step-by-step instructions.
Start by opening Windows Explorer where you can see the zip file (probably in your Downloads folder).
Then right-click on the file and select "Open With" out of the drop down menu and then select "Windows Explorer" out of the second drop down menu. It will look something like this:
When this opens you should see something like this:
Select the rms file, click on the "Extract" tab, and select "Extract to".
Then choose a location. You'll find the rms file there.