For users reauthorizing copies of ArcGIS already installed on their machine, visit http://esri.com/educationedition to register your license code with Esri, then open ArcGIS Administrator (located in the ArcGIS program group in the Start menu). Click on the Desktop folder in the left-hand pane, select the Advanced (ArcInfo) Single Use option, then click Authorize No​w. The reauthorization procedure will be similar to the process that begins in step 8. 

If you need to uninstall and reinstall your authorized copy of ArcGIS (for example, if you are reformatting your hard drive or switching to a new computer or you have entered your eva code in once and it did not authorize) please follow these instructions before uninstalling the software.