change the pace of the grid

Hello
I am a beginner on LibreCad and I can not change the pace of the grid that I want to adjust to 1mm or 0.5 mm.
How should I produce?

The grid spacing can be 'fixed' in the Drawing Preferences.  From the menu, select Options->Current Drawing Preferences, select the Grid tab and specify the X Spacing and Y Spacing.  Also note that the Units (as defined on the Units tab) will affect the appearance of the grid.

thanks to you
It seems to work

Thanks Gary S
This only worked after saving the file and opening it again.
But it work