At the moment, Yedda staff are the only ones who can permanently erase a posted question.
To request they do so, please use the Feedback link found at the upper right corner of your screen. Once that page loads, select the appropriate topic from the pull-down menu and then type your request in the accompanying text box.
(Please be sure to let Yedda staff know the reason for your request.)
Allow up to two weeks for staff to receive and process your request, as they get a lot of mail and yours will have to wait its turn in the queue.
In the meantime, you can make use of the 'Edit' function in whatever question you wish to delete.
Simply open the question and click on the 'Edit' link. Then use the backspace key to erase the existing text and/or replace the text with something else (random characters, numbers or so on).
Please keep in mind that this will not erase answers to your question, so Yedda members will still be able to see and respond to it based on the existing visible answers.