The following steps will help you change the text size.
Step 1 − Select the text the case of which you want to change.
Step 2 − Go to the Font group under the Home ribbon.
Step 3 − From the Font Size dropdown, select the size you want to use for your text.
Step 4 − Click on your choice to change the font size for the selected portion of text.
Step 5 − If you want to change the font size in steps you can also use the Increase/ Decrease Font Size options.