How to remove some roof tiles

[blueagle78]

I've got a studio flat on the ground floor in my house and its really cold during winters. 3 walls are exposed and part of the roof is exposed too. Its got wood floor which doesn't help the cause either. Luckily walls are properly insulated but roof isn't. I've got some insulation in the loft which I could use to insulate the exposed roof but I don't know what's the best way of removing some roof tiles to get access to it.
I've marked the area in red in the below picture which is exposed and needs to be accessed.

Any advise would be greatly appreciated. Thanks

 

[joe-90]

Probably easier to take down some plasterboard from below.

 

[blueagle78]

Oh, is it? I think I won't be touching the inside because its all nicely decorated plus got quite a few spotlights.

 

[Lower]

Better to take down so plasterboard now than replace it anyway later when it's water stained due to a leaking roof.

Is there no access to the void from upstairs?

 

[blueagle78]

There is but its pain to access. I think I'll take that route because I'm not willing to risk either leakage or decorating the indoors.
I've got quite a few spot lights and I'm thinking of covering them with flower pots (as I've read it works out fairly well on few forums) to make sure insulation doesn't cover them. I guess this is the most cost effective way or doing it?