I would wait untill all cances of frost have gone and new growth is visable. Make sure they are brown and dead and dont remove and green ones.
Has it been covered up over this cold winter?!

Hi,only covered the trunk with fleece. The fronts are still nice and green,I tied them together,so that the top of the trunk does not get too cold. The fronts are only a little bit brown around the edges!

I would just leave the fronds then untill they completely turn brown and naturally droop. This will make way for the new fronds to grow.
Although they may be brown around edges as they have suffered from the cold. Some people tie the fronds up and wrap from trunk up to the tips of the fronds. This normally keeps them green and therefore last abit longer before they naturall drop.
Aslong as the crown, where the new fronds grow from, is well covered and kept frost free then all will be well!

Thanks for your good advice, better than from books.Short,simple and straight to the point, that's what I like!!