Is not all that much work, I did it by undoing the cooler line and let her drain out.
I heard u can also drain the torque converter too. Thats a bit too much work for me.
U should feel the car more responsive after new oil, more rev happy.
one vOLVO I had , the tranny oil was real bad, kind of seeing some semi solids too, wonder how she had carried me all these miles. the car felt much lighten up after.
U don't need to change it all to see improv.
I used the old oil as oil spray in lieu if WD40. Funnel her into a oold spray bottle. Use in non critical application. A lot of door hinges, everyday lube job etc doesn't need Military grade clean oil anyways.

When u fill up, be a little careful, can overfill quite easy.