To edit the label properties for contour map labels in Surfer:

1. Select your Contours layer in the Contents window.
2. Click on the Levels tab in the Properties window.
3. Check the Level method at the top of the General section. 
   • If the Level method is set to Simple or Logarithmic,
     1. Scroll down to the Labels section.
     2. Expand the Font properties section.
     3. Set the desired font properties.
   • If the Level method is set to Advanced,
     1. Click the Edit Levels button.
     2. In the Levels for Map dialog, click the Label column header.
     3. In the Labels dialog, click the Font button.
     4. In the Font Properties dialog, change the desired font properties.
     5. Click OK in the Font Properties dialog.
     6. Click OK in the Labels dialog.
     7. Click OK in the Levels for Map dialog.

See here for instructions on how to change contour map label properties via automation.

Updated October 20, 2021