There are several differrent styles of bullet points in MS Word, you can even add your own picture or custom bullet point. If you want solid round bullet points (the normal bullet points) they should populate automatically, but if they dont, select/highlight the "square bullets" then go to the Home tab in the paragraph section and click on the drop down box beside the "bullets" button. Then click on the round, solid black bullet point to select it.
If you try this and it does not work, try printing a test sheet to see if they are printing in a circle or a square format. It could possibly be the photo resolution of your screen that is making the round bullet points look like they are square.
If that doesnt work, save your document, exit out of word and open it back up. I've never heard of the defualt bullet points not working, but sometimes weird stuff happens.