Decompile/Recompile apk's with ApkTool

You need to have 

1. apktool / aapt, which can be downloaded from code.google.com (Click this link !)
2. Java Runtime Environment(JRE), normally you would have it in your PC. It should be atleast 1.6, make sure to add this in your windows path variables. If you don't have it, then Google !
3. Follow the instructions on the code.google.com to install the apktool and aapt, and unzip them to windows folder. On a windows system it is done like this (copied from the site, you can as well look there for other OS)
• Download apktool-install-windows-* file
• Download apktool-* file
• Unpack both to your Windows directory
4. Now your apktool is ready to use.

Now first things you need to do for decompile any APK is that, to have the framework file for that APK. apktool comes with the standard framework, so you need to execute the following command to get the framework required for decoding.

apktool if your_application.apk

You would get some message like below.

I: Framework installed to: /home/brutall/apktool/framework/2.apk

For more information about these framework files you can refer to google website here. (FrameworkFiles)

Now create a folder for you work, and place your_application.apk file in that folder, and open the command prompt and cd to that folder, and run the following command, you apk would be decompiled. 

apktool d your_application.apk your_application

This would create a folder named your_application with xml, resources, images etc. You can change whatever you want to  (if you know how to change! else do some experiment)

Now that you have changed you can pack them back to apk using apktool, run the following command. 

apktool b your_application your_applicationNew.apk

Now, as you know that signature would be different in this new APK, you have to open both these New and  original APK in a zip manager such as 7zip/Winzip and replace the images if at all you changed into the respective folder inside zip file, and also resources.arsc files.

This would complete the change, you can place it back where ever your apk was before, and ENJOY !!

Feel free to leave a message if it helped you in any way, and also let me know if you face any issues, would love to guide you. A Thanks would cheer me for writing more such posts :)