1996 discovery,im have trouble shifting in gear or out of gear ,i think it's in high. i can't get the shifter to move.

 

if you can go over 30mph then it's in high. try greasing the shift linkage underneath the rover and work the shifter to loosen it up.

 

It can be very stiff if you don't shift it into low often. Spraying a little PB blaster or WD 40 at the shifter linkage and trying to shift it a few times with force can help break it free then put some sort of lubrication on it. If you are pushing with all your might there is a solenoid that goes bad that can prevent you from shifting and it would need to be replaced.

 

or removed

 

make sure when shifting you are either:

1. rolling in neutral
2. sitting still in neutral but pushing on the gas

 

To clear up this statement, never push with all your might, you will bend or brake the linkage.
You either need to get the linkage assembly cleaned and lubed or remove/replace the shift solenoid.