delete undeletable image folder

I use an Iphone 4 and have been facing terrible space issues recently. There are three folders I want to delete (synced from previous Android phone) and these, I figured out cannot be deleted using the Iphone.

I plugged it ti my PC, launhed itunes and did the regular sync photos and tried syncing a blank folder - the quickest trick most websites suggest.

But these three folders do not eveb appear in the drop down for me to select and syc with a blank folder,

Pls pls pls help