Matlab differential smoothing slider for multiple lines in plot

Hi I am wondering if someone could help me with this problem...

I have made a GUI to import and plot multiple file, here is the code:

    d= uigetdir(pwd, 'Select a folder');

    files = dir(fullfile(d, '*.txt'));

        len = length(files);

        linecolors = jet(len);

        for i = 1:len

        a = files(i).name;

        filename{i} = a;

        path = [d,'\',a];

        data = dlmread(path);

        plot(data(:,1), data(:,2),'color',linecolors(i,:),'linewidth',2);

    hold on;

    end

    hold off;

I would now like to smooth the lines, but how do I go about smoothing multiple lines in a plot?

The smoothing method I would like to use is where the differential between two points is found and that gradient is plotted. Is there a built in matlab function for this?

I would also like to vary the amount of smoothing i.e. finding the differential 1/2/3 etc.. times over. Would I be able to make a slider for this? Or else allow the user to enter in a number for the number of times they want the differential to be taken?

If you don't know specifically how I can go about coding this, I would still be grateful if you could point me in the right direction :)