How to avoid duplicate uploaded file?

[eluser]solid9[/eluser]
Hi guys

I want to avoid duplicate uploaded file names.
But what CI did was it duplicate the name and extended
the name with numbers like this below,

Code:

android.jpg
android1.jpg
android2.jpg
android3.jpg
and so on...

How to avoid this duplicate files but instead just replace the
existing the same file with new file?

Thanks in advanced.