Here's how to remove all labels and how to restore default labels
% Create demo GraphPlot
s = [1 1 2 2 3 4 5 5];
t = [2 3 3 4 4 5 1 2];
G = digraph(s,t);
h = plot(G); % Store handle!
labelnode(h,[1 2],{'source' 'target'})
% To reset labels
h.NodeLabelMode = 'auto';
% To remove all labels
h.NodeLabel = {};
