Thanks Lightsplasher for your answer.

My greencoin are actually on coinexchange and not on yobit because I can't open a wallet on Yobit. If I sell on coinexchange I would lost because the sell price is too low. So I keep them on coinexchange and I hope they will update on yobit or for for dreaming a bit on bittrex ( or poliniex)

By the way if you have any advice to sell them at the right price i would appreciate thks