Delete email folders in yahoo??

I use yahoo mail and in addition to the inbox, sent box, etc..I've created quite a few folders which all got downloaded to the iphone when I synced it the first time..

Is there a way to delete these folders? I can delete the emails within the folders, but haven't figured out how to delete the folders themseves..as I don't need them on my iphone..but then even if I delete them, will they appear again every time i sync my phone in order to get new itunes i've downloaded into itunes on my computer? Thanks...