Cannot figure out how to close thread in sale section

I've read the guideline and the right section about closing threads in the selling section in Ventar's corner, but I still do not understand how to close a thread there. Can someone explain? :/

Thread tools - Edit Thread - Change the prefix to closed in the dropdown to the left of the thread title.

Don't edit the text in the post though,the prefix change is enough.

check out the last post in this thread: http://www.guildwarsguru.com/forum/f...t10388139.html
it even includes screens to show you how to do it.

Thank you so much! Closed my thread now