After successfully downgrading from 4.2.1 to 4.1,Now you will of course need to jailbreak your iDevice.
This tutorial will help you to jailbreak your iDevice. This is very
simple and easy tutorial that will neither interfere with your baseband
nor it will unlock your iDevice. It will just simply jailbreak it.
An iPhone with freshly restore iOS 4.1
Limera1n click here
Step1. Connect your iDevice with Pc and Open the downloaded limera1n.
Step 2: Click on make it rain.it will reboot your iDevice and will enter into recovery state.
Step 3: Follow the instructions on the screen.
Ist hold the home and sleep button than leave the sleep button and holding the home button.
Step 4: After sometime a popup will show on your screen as shown below
Step 5:iDevice will reboot and an icon either like this
Or like this will be shown
Step 6: Click on the icon and install the cydia.
Note: you must be connected with wifi for this Operation. Finally,
you have successfully done your jailbreak on iOS 4.1. Please share and