Hi I need some advice can I change the Rx and Tx on board LED to bigger LED???
By "bigger" do you mean physically bigger or just brighter? I'm afraid that if you choose a larger package size it won't fit properly on the surface mount pads on the PCB...
And why would you want to change them anyway? You can wire up LED's to the Arduino separately for indication. The RX and TX LED's are mainly meant to provide visuals for serial communication, like when you're uploading code or entering something in the serial monitor.
yes you can, parallel 180 ohm to 1k build in smd resistor to add current to 20mA
If you really want to make them brighter, swap out the 1k resistors in series with the LED's to a lower value, like 330 Ohms to give it more current, but why would you parallel resistors? That sounds like more work than just swapping them out.
Orange LED's typically have a forward voltage of around 2V and draw 20mA, and since they're powered by 5V that means you should choose a resistor that is at least R = (5V - 2V) / 0.02A = 150 Ohms. To be safe, choose something like 250 or 330.
How good are your soldering skills?
Yes, I was going to ask that - how good are you surface-mount rework skills? If not good you
risk lifting pads and breaking the board.
aarg:
How good are your soldering skills?
I'm pretty good in soldering sir. So can i change the Rx led to LED so I can add , more drama to my circuit?
You should replace the resistors, not the LED's.
androidfanboy:
You should replace the resistors, not the LED's.
Why sir?
will it damage my arduino if i tried to change the RX and TX led???
You haven't really explained your project. Will the new LED's be situated off-board?
Yes, you can. The end. Come back if you have any more questions. Good luck.
The Arduino project gives you permission to change the LEDs. (Read the licence thoroughly if you care.)
You are the one holding the soldering iron. The possibility of damaging the board is entirely in your hands.
Yes, but only if you STOP SHOUTING! :o
// Per.
Zapro:
Yes, but only if you STOP SHOUTING! :o// Per.
Sorry sir 
I naively thought that an external LED on either of pins 0 or 1 would follow the built in Rx and Tx LEDs. Luckily before suggesting that, I tested and that's not the case. Can someone explain why it's not the case?
So you did connect an external LED (with current limiting resistor) between 5volt and pin, and it did not work?
Don't expect it to work between pin and ground, since these are TTL outputs.
Leo..
Wawa:
So you did connect an external LED (with current limiting resistor) between 5volt and pin, and it did not work?Don't expect it to work between pin and ground, since these are TTL outputs.
Leo..
If that was at me, hmmm no, it was from the pin to ground not 5V to pin.
And indeed, when I put the LED and its resistor from 5V to the Tx pin, it does flash along with the builtin one, when my sketch does a Serial.print.
So @OP why not just use an external LED/resistor and save buggering around with microscopic soldering?