1. In Formatting Property click on Legend Property.

2. The Legend font properties used to control the legend text appearance in chart widget.

3. Enter following details in Legend font Properties:
Font Family: Times New Roman
Font Size: 12
Font Weight: Bold

4. Fill above details, As shown in figure below:

5. Click on Preview and Save and Exit.

6. Now, match your Radar chart with the below example, it should look like the figure below: