Just use a small set of long skinny nippers or something like nose-hair scissors. Just nip it above the junction of the two sets of leaves {at whatever node you decide on}. But most of the time I forget to pack my little nipper thing, so I pinch them off with my thumb and finger. It's very tender, it will come off with little resistance.
I was out checking on my GN patch yesterday when I discovered a BST2 that was over knee high and hadn't been topped. Not sure what I was thinking the last time I was out there. But it can be put in the better late than never category, it's topped now.