Taking the window unit out is a doddle, only a few beads to clip out and they just lift out, usully with those suction pads.....however....beware......
About 10 years ago, I was offered a brand spanker leather suite, kind of an ask no questions, get no lies type of scenario....I had no idea of its origin, but it arrived in an unmarked van, and because it wouldn't fit round the hall etc, the window had to be removed.
My mate came round and took out the unit. it was a big window, covered most of the front of the house, but it came out pretty easily. Suite came in through the window no bother, but when it came to putting the glass unit back in, my mate had a terrible time fitting it in....turned out when the window had been fitted (prior to me owning the house), the fitters scrimped on it and never put in a lintel above it. So with the window out, the whole of the front of the house bricks dropped, hence the window not going back in easily. When back in, looking at the front of the house, you could visibly see a sag curve in the bricks. It ended up costing me £3k to get it fixed....so the few hundered quid I save on the suite, was wiped out somewhat, and I put it down to a lesson learnt.