On the My Snipes page click on the Folders: button (on the right, near the top).
In the Folders & Bidgroups box is a list of your folders and bidgroups. On the right of each are two (not very obvious IMHO!) options - update and delete. Use these to update and/or delete your folders.
nb. Always, always delete a bidgroup folder after use as it cannot be re-used after it has been successful!