Microsoft Edge comes packaged with the Windows 10 operating system. This means that you'll need to update Windows to get the latest version of Edge. For most Windows users this should happen automatically, however some organizations have disabled automatic updates for their users. If your device is controlled by your school, you may need support from your IT representative to update software on your device.
For Windows 10 users, to check for updates you'll need to click the Start button, and then go to Settings > Update & Security > Windows Update.
From there you should be able to follow the directions to update your device.
For more information head over to Microsoft's guide to updating Windows 10.