You can change the font size of the tick labels by setting the FontSize property of the Axes object. The FontSize property affects the tick labels and any axis labels. If you want the axis labels to be a different size than the tick labels, then create the axis labels after setting the font size for the rest of the axes text.
For example, access the current Axes object using the gca function. Use dot notation to set the FontSize property for the Axes object. Then create an x-axis label with a different font size.
x = rand(1,100);
y = rand(1,100);
ax = gca;
ax.FontSize = 16;