how do I remove the 4 didget passcode from my ipod , I forgot the code

You need to Restore it in iTunes with the last computer you synced with.

Connect the iOS device to your computer and restore via iTunes. Place the iPod in Recovery Mode if necessary to allow the restore.

If recovery mode does not work try DFU mode.

How to put iPod touch / iPhone into DFU mode « Karthik's scribblings

For how to restore:

iTunes: Backing up, updating, and restoring iOS software

To restore from backup see:

iOS: How to back up

If you restore from iCloud backup the apps will be automatically downloaded. If you restore from iTunes backup the apps and music have to be in the iTunes library since synced media like apps and music are not included in the iPod backup that iTunes makes.

You can redownload iTuns purchases by:

Downloading past purchases from the App Store, iBookstore, and iTunes Store