Step 1: Go to Dashboard
Step 2: Click on the tab labelled, "Design" and click on "Template Designer"
Step 4: You will now see a list of options for personalizing your blog. Here you can change the colors of your links, titles, text, etc. To change the font, scroll down, where you will see a list of font options for the title, sidebar, text, description, and footer.
Here is an example of how it looks when I change the font for my title.
And a view of the preview:
Now, on the top across from "Blogger Template Designer," you will see an orange button, "Apply to Blog." Click on it, and it should work right away. Preview your blog to see if it worked.
Congratulations! You have successfully changed your fonts in your blog. Have fun personalizing your blog in the future, the possibilities are endless!