Not really sure if I understood your question, but if you want less data points within the same interval, then just use interp1. Here is one example:
close all
x = linspace(0, 10, 100); % 100 points between 0 and 10
y = sin(x * 2);
plot(x,y)
hold on
% 2 times smaller in size
xi = linspace (0,10,50); % 50 points between 0 and 10
yi = interp1(x, y, xi, 'linear');
plot(xi,yi,'r')
