Hi,
You can change the decimal precision using the label style composer for the contour label type.
In the Prospector Settings tab, expand the Surface collection, the Label Styles folder, and then the Contour folder. Select the contour label style, right-click and click Edit. In the Label Style Composer, select the Layout tab. In the Text property group, click the Contents field and click the ellipsis to open the Text Component Editor. For the Surface Elevation Properties, you will see a Precision modifier, which you can change to your required precision.
Regards,
Jonathan Burgoyne,
Autodesk