Hereís a thread with detailed instructions:
I just did this job, hereís the short version:
Slide window all the way forward.
Remove the channel material, at least the top section for now.
Slide the window back, lift and wiggle until the bottom of the window clears the aluminum track and you can bring the window inside with you. Donít force it, and above all donít drop it.
There are other threads on this, do an internet search for ďsliding window site:airforums.comĒ