To view some applications you may acquire more space on your Mac screen. So, it is very simple to quickly change the size of Dock on Mac OS X and the method is as follows.

Step 1

See on right side of your Dock there is a bright doted line which separates Recycle Bin & opened running applications from other icons

Step 2

Just take your mouse pointer on those bright dots line and cursor will turn into a resizing cursor. Hold the mouse button and drag it upward to increase the size of Dock and drag downward to decrease the size of Dock.

So, this is the quick way to increase or decrease the size of Dock icons. See also Customize the Dock.