to delete channels, buckets or videos simply drag and drop them onto the trashcan icon within the tool bar.

while on the welcome-screen you can d&d channel-icons only.
while in clipboard- or playlist-view you can d&d video- and bucket-icons but no channel- (root-) icons.

deleted buckets and channels will be deleted immediately.
videos and/or videos still contained in deleted channels or buckets will land into your trashcan.

you should frequently empty your trashcan (but you don´t have to).
trashed videos can be recycled and will be put into your clipboard then.