I don't really think you can just increase the size of the icons in the
taskbar alone.  You can however adjust your display settings and see if you
can accomplish something close to what you are after.  Right-click anywhere
on your desktop in a blank area of the screen and select Properties.

Good Luck

I should add that if you adjust your screen area size in the display
settings, that it will make icons, text, graphics, everything larger or
smaller.  I would adjust this setting first and find one that meets your
needs.  You can then go in and individually adjust your text sizes.  But I
believe that  the icons are automatically adjusted with your font or text
size and there are no manual controls.