Remastersys, it is free tool for it
you can install it via ppa

You can find more info here remastersys forum

Installation instructions quoted from remastersys forum.

The Synaptic Method:

1. In Firefox, go to:

   
   
   

   http://www.remastersys.com/ubuntu/remastersys.gpg.key
   save file as text someplace where you can find it.




2. In synaptic, go to Settings/Repositories; select "Authentication" tab and "Import Key File" just downloaded.




3. Still in synaptic, go to "Other Software" tab and click "Add", then enter the apt line and replace oneiric with either lucid,
   maverick, or natty to match your Ubuntu version:

   
   
   

   deb http://www.remastersys.com/ubuntu oneiric main




4. Leave the repositories tab and "Reload".




5. Search for "remastersys" and select for install. Edit/Apply Marked Changes.

The Manual Method

Download and apply the repository signing key.

wget -O - http://www.remastersys.com/ubuntu/remastersys.gpg.key | sudo apt-key add -

Add the following line to your /etc/apt/sources.list, substituting "oneiric"
for your Ubuntu version (e.g. lucid, natty, maverick)

deb http://www.remastersys.com/ubuntu oneiric main

Now just sudo apt-get update or reload in Synaptic to have the new
Remastersys signed repository ready to use!