A 20x4 LCD display is a very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations, and so on.
A 20x4 LCD means it can display 20 characters per line and there are 4 such lines. In this LCD each character is displayed in a 5x7 pixel matrix. This LCD has two registers, namely, Command and Data. This is a standard HD44780 controller LCD.
There is no change code for interfacing standard 16x2 or 20x4 LCD.