Care of a Poinsettia Tree?

I am English, but live in southern Spain and just before Christmas was given a beautiful poinsettia tree. It is about 100cm (40 inches) tall and the top 2/3 has bright red bracts. It is in a pot 20cm (8 inches) wide. It stands near a window, good light but no direct sunlight. I water it about once a week.

However, this last week or so it has started dropping leaves, several a day and I am concerned about its future care. We never get frosts and winter temperature is fairly mild, usually high 50s low 60sF, seldom below 50F (8C).

We have a large very sunny terrace and could keep it there in a larger pot, which I would prefer or it could go in a smaller lawn area in the ground, but there is not much room there and it's not sunny all day as on the terrace. Which would be best? I have read a lot about these plants needing lots of dark time (overnight), but can it stand the hot sun we get in the summer?

Should it be pruned at all, if so, at what stage? Any help anyone can give us would be much appreciated as we would not like to lose this lovely plant/tree. Thank you.

By Jackie W.