We just did this to install a fridge. What WHALER2 describes is very accurate. Using a strong plastic tool, go all the way around the window where it meets the side of the RV. There is double sided tape in that 1 to 1.5" wide window frame gluing the window to the RV. Once you've broken that bond, then you'll need to slowly bend the inside rubber seal so you can "push" the window out. Only push on the metal frame, not the glass. The rubber seal moves with the metal frame. This is where the soaped rope comment fits in.
I hope this helps.
2003 National Tradewinds 375 LE