When a new version of Internet Explorer is released, your browser will prompt you to update it. If you do not accept this update, you may have issues using certain websites. If the website lists which version of Internet Explorer the site is viewed best with, and you don't know if you have that version, you can check using the top menu bar.
Open Internet Explorer.
Click on "Help" in the top menu bar.
Click "About Internet Explorer" to see which version you are using.