I have actually done this. The best idea is to take the whole frame off otherwise the roof will start to crack when taking it off.
This is how I did it. When the roof is up, inside the car under the lining in the back either side it the bolts holding the motor pistons in place. Undo these and take the pistons off the bracket thing on the roof. Then push the button to put the roof down so the piston will go down - this is to stop them from ripping the roof when you fold it down later.
Around the edge of the back of the roof inside, there will be 2 small nuts on either side. Near to where the back window is. Undo these, making sure that you dont drop them down the hole.
After this undo the tensioning nuts holding the roof around the back. Once these have all been undone and the tension wire has been taken out of the bracket, you can pull all of the roof from out the lip outsde the car.
When you have pulled out all of the roof from the lip, you can see the two bits of roof that give the back tension joined onto the back of the car. You have to try and get the bars out from the holes to release these. It took me quite a while to get them out from mine.
Once you have done all of this, fold the roof down manually and you should be able to see the 3 bolts holding the brackets for the roof down on either side behind where the speakers in the back are. Undo these 3 bolts with side. Once this has been done, the roof should technically lift off.
Putting the roof back on is the opposite from taking it off.
Hope that this helps, sorry if it isnt very clear, I cant really remember what I did now but that is the basics. I may be able to offer more advice if needed. Taking the roof off took me a couple of hours first of all but after doing it once it was pretty easy and took alot less.
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