First things first, make sure you're in your Profile.
In the Education section, hover over the education history you'd like to edit.
Click on the Edit (pen) button, and a drawer will slide out from the right.
When you're all done, be sure to Save your change!
To cancel any changes you've made, simply click the left arrow in the top bar. You will be prompted "You have unsaved changes. Are you sure you want to leave without saving?" Just click 'OK' and your changes will not save.