Stop everything you are doing. Go to www.jeep.com
, download your owner's manual and read the entire 4WD section. You should never try to force it into 4WD. There is a plastic grommet that connects your cable to the TC. It is meant to break to protect the TC if you try forcing it into gear.
If you are in 4H and are stuck, putting it in 4L isn't going to do anything to get you unstuck. 4L is just lower gearing. 4WD is 4WD.