Hi @Anonymous and welcome to the Autodesk Community!
Yes, you can install the 2015 student version of Revit after having installed the 2014 version. All you need to do is download the 2015 version from the Education Community, and activate it using the serial number and product key provided by the Education Community for the 2015 version.
Please accept as solution if my post fully resolves your issue, or reply with additional details if the problem persists.
Camilo Lemos