Modifying Unit :
Tools>options>Units from the menu bar .
You can set the units for length,angle,time,mass and so on,using the option in the unit dialogue box.

Modifying the grid setting :
Tools>options>mechanical design> sketcher from the menu bar.
You can change the value of graduation and primary spacing.The spacing between two dotted line is called graduation ,while the spacing between the two continuous black line is called primary spacing.