Trouble changing units

I'm in mm. I go to Application Preference->Defaults-> unit: inch
I go to Drawing Preferences-> Inch
but it does not change units.

Also, I have forgotten how to get cross hatching in a given area.

What exactly is the problem? Does it not accept the change in the input tabs and stays saying mm? Did you just close the box with x button or did you click OK? Have you saved the drawing when leaving?
Or do you expect the mm to be recalculated to inches? That doesn't happen, you have to scale the drawing manually with the according factor. I have already explained this.  

What exactly is the problem? I will go into more detail for you below.
Does it not accept the change in the input tabs and stays saying mm?  It accepts the two input tabs, saying Inch in both places.
Did you just close the box with x button or did you click OK? I definitely use OK in both places
Have you saved the drawing when leaving?  yes I reopen the drawing. It shows "Inch" in both places, but the units at the bottom of the page still show as "mm." When I add a new feature  in the main window in shows as mm also.
you have to scale the drawing manually with the according factor. I don't understand this last statement. What does "scale the drawing manually" mean?   What is "according factor?"

Ah, now I think I might have a clue what the problem is. At Drawing Preferences - Units you also have to change Length - Format to something different than Decimal. Engineering, Architectural or Fractional. Also have a look at Precision.

 "scale the drawing manually": let's say you have an object 100 mm long drawn in mm. Now you want to change the drawing into inches. It will be 100/25.4 = 3.937 inches. So you have to scale the whole drawing with the factor 1/25.4. But probably that's not your issue.

I'm sending two images, one on the units page & one on the dimensions page. The units at the bottom show as " after changing to engineering, but when I use dimension, it still gives me numbers in mm. I tried changing the scale to 1/25.4, now I get two vertical lines on the left far side & right far side - no arrows & no numbers showing. Further advice needed.

Also, how do I add cross-hatching inside a drawing area.

Also in Dimensions you have to change Format units - Linear units from Decimal to Engineering.

At General Scale you can set the inverted value of the printing scale. For instance, if the drawing is to be printed at 1:5, you write 5. Then the values set in inches for Text Height, Dimension line gap, Offset, Enlarge, Arrow or Tick size will truly have that size on paper. So don't write 1/25.4 there. If your drawing is to be in 1:1 scale, write 1.

For hatching there must be an enclosed entity, like a rectangle, a polygon, a circle or polyline. Click on the hatch button, then click on the entity or all of its elements, close the selection with Enter. The Choose Hatch Attributes box will appear, select your hatch (for cross hatch "Plastic" may fit), experiment with Scale and Angle, then Enter or OK.

Well I've made some progress - I can now do hatching. However, I'm still getting 3 mm & 5 mm when dimensioned, i.e. the objects are actually 3 mm & 5 mm. Making the changes you recommended shouldn't the software convert those values to 3/25.4=0.12" & 5/25.4=0.20"?

Now let's assume you have intentionally designed and drawn the part in mm. Now you want a plan variant with (same) size expressed in inches. Internally LibreCAD thinks in units only. If you change the settings to inches, it in fact just changes the "name" of the units. So 5 mm become 5 inches. To get the inch values right you have to scale the whole drawing by the factor 1/25.4.
Go to Tools - Select - Select All or pull up a window around all drawing entities, then do Tools - Modify - Scale, select the reference point, in your case probably absolute zero (0,0), in the input box tick Delete Original and Isotropic Scaling, and write 1/25.4 as factor, hit OK.
The following dimension settings may be appropriate then: