From the file menu choose Insert, Picture, then WordArt.
You will then see the word art box.
First row third icon is an arc. Select it by clicking on it. Click OK and you will see the words ... YOUR TEXT HERE.
Change the font to 8 point size and select whatever font you want and type the words you want. Click OK. I suggest that you type your words at least TWICE, i.e. Happy Birthday, Happy Birthday.
Your words that you typed will now appear on the "page".
Highlight your phrase on the page by LEFT clicking on your mouse once.
You will see a drop down box appear at the top of your page that says Word Art.
Look for the blue ABC icon (should be the 5th icon across in the box) in the drop down menu.
A box will open with all sorts of shapes. Select the circle by clicking on it (there are many shapes to choose from - experiment with the others later). Your words will now appear on the page, all smushed together.
LEFT click ONCE on the words on the page that are all smushed up.
Then click on format at the top in your toolbar, click on word art, a box will appear and you will select the size tab.
Then make it whatever size you want ... text in a perfect circle.