If the header is too long, just cut/snap it short!
Next you'll need to solder the header to the LCD.You must do this, it is not OK to just try to 'press fit' the LCD!
Also watch out not to apply too much heat, or you may melt the underlying breadboard. You can try 'tacking' pin 1 and pin 16 and then removing from the breadboard to finish the remaining solder points
The good news is that not all these pins are necessary for us to connect to the microcontroller (Arduino). RW for example, is not needed if we're only writing to the display (which is the most common thing to do anyways) so we can 'tie' it to ground. There is also a way to talk to the LCD using only 4 data pins instead of 8. This saves us 4 pins! Why would you ever want to use 8 when you could use 4? We're not 100% sure but we think that in some cases its faster to use 8 - it takes twice as long to use 4 - and that speed is important. For us, the speed isn't so important so we'll save some pins!
So to recap, we need 6 pins: RS, EN, D7, D6, D5, and D4 to talk to the LCD.
We'll be using the LiquidCrystal library to talk to the LCD so a lot of the annoying work of setting pins and such is taken care of. Another nice thing about this library is that you can use any Arduino pin to connect to the LCD pins. So after you go through this guide, you'll find it easy to swap around the pins if necessary