First of all you will most likely have window guides
that look like this. They were white, or off white, back in the day.
Airstream now sells them in black.
That is a good thing as they do not show dirt as well.

Open the window and let it rest on any one of the good guide slots that are able to hold it open.

The handle on the inside must be removed. It is attached by a hex-head screw in the bottom.

Detach the support arm using a 5/16 wrench or ratchet .

Remove the support arm. Repeat for the right side of the window.

When ever I have done this job by myself, I have put a towel or cushion on my head to hold the window up. Or I would use a long board on the ground, so I could continue to work.

Drill out the rivets that are holding the broken guide in place.

Make sure that you have a small drill bit so that you don't make the hole to large. If your drill bit is smaller than the hole, that is ok. You can always re drill and make it larger. You can't make the hole smaller if you make it too large. Most of the time it is a #30 drill bit.

Hold the new guide in place.

Rivet the new guide in place. The holes in your window jam may not line up perfectly with your new window guide. You can use your new guide at a template to drill the 3 other holes if they need it. I have found it works best to do the top and bottom hole first. They most likely won't need drilling. Then drill the other two if need be.

Replace the support arm.

Reattach the support arm to the window,
and put the inside knob back into place.