For older versions you have to proceed like this :
Close the arduino 0.2.2 GUI.
Find and open "preferences.txt".
This can be found at :
Documents and Settings/[username]/Application Data/Arduino/preferences.txt (on Windows XP)
Users/[username]/AppData/Roaming/Arduino/preferences.txt (on Windows Vista / Win7)
~/Library/Arduino/preferences.txt (on Mac OS X)
~/.Arduino/preferences.txt (on Linux)
Find the line :
and change it to :
If you are using other external programmers the choices are :
These programmers values can be found at "hardware\arduino\programmers.txt"
Save and close the "preferences.txt" file.
Now by hitting the "Upload" button you are uploading the sketches using the external programmer.
A more detailed tutorial can be found at the official web site.
Again by doing this you are erasing the bootloader.
In order to re - use arduino normally you have to re-edit "preferences.txt" and change the "upload.using" :
You'll also need to burn the bootloader back onto the chip on the Arduino board.
In the video below we can see :
1) Arduino is connected with usb tiny, our external programmer.
The external programmer is connected to the PC .
We upload successfully the arduino blink sketch but we lose the bootloader.
2) We connect arduino directly to the PC.
The external programmer is disconnected from arduino.
We can see that we are not able to upload any sketches.
3) We reconnect the programmer to the PC and the programmer with the arduino board via the ICSP header.
We burn the ATMEGA with our new bootloader.
4) Now if we connect arduino directly on the PC removing the usb tiny we can upload our sketches normally.