You can add or delete any new Groups created by you, there is a Sticky thread about that.
But can you can not delete the excisting Groups that are seen thru LiveTV or VODs
Only way really would be that you could get a hard copy of the Playlist (LiveTV and VODs) and open that list for editing thru Notepad editor on your PC's desktop.
Then remove the channels you want to remove and save the work.
Use that edited hard copy thru the Playlist setup menus.
You can add EPG Urls in there as well.
There is a downside to this thou.
If and when there are channel changes done at the service level, then you would not see those changes until you get a new hardcopy from the service and do the editing again and then use that copy.
It is not as difficult as it sounds and if wanting to remove a category for good reason, like the 'Adults' category so your children do not accidentally open those channels, then it might be well worth the effort
But also you can add or change the lock out password for any channel.
One thing to note is that them PPV channels get updated with changes often and with the hardcopy that was not updated, you'd still get the new selections that were added, but it would be that you would not see the new names of the channel, they'd always show the name as it was when you downloaded the hardcopy.
I did not know you could delete Groups from other models