Here's how you can manage your data stored at COB storage removing data that you don't need and freeing space for new backups:
Click "Restore" -> Select any snapshot -> Click "Remove"

Then select one of options:
- Remove current snapshot
- Remove selected files from current snaphot only
- Remove selected files from all snapshots (i.e. all versions of these files)
- Remove several snapshots at once (advanced snapshot removal)
- Remove whole computer
To remove several snapshots at once select "advanced snapshot removal":

You can select several snapshots and click "Calculate free space" to find out how much space will be freed if they will be deleted. "Remove selected" will actually delete them.