The operation method of changing font size in CAD is as follows:

1. Click the text to be modified first, and a blue dot will appear after activation. As shown in the figure below:

2. Then click the "A+ Pen" icon in the upper right corner, as shown in the following figure:

3. After the text style dialog box pops up, click Height to enter the required text height, then click Set as Current, and finally click Apply. As shown in the figure below:

4. Finally, click Close to close the Text Style Settings dialog box. As shown in the figure below:

5. Finally, the font size was changed. As shown in the figure below: