You seem to be dividing the axis scale by 5. The same steps also apply to 'XTickLabel'
ylabel = get(gca, 'YTickLabel') % returns 5x2 char array
ylabel =
0
20
40
60
80
newylabel = num2str( str2num(ylabel) ./ 5 )
newylabel =
0
4
8
12
16
set(gca, 'YTickLabel', newylabel);