More often than not, the information provided in an EndNote reference is full and correct, therefore references do not need to be edited. Occasionally information is missing or incorrect, or more frequently, EndNote users want to add their own notes or keywords to help them find specific articles or types of articles later on. For instance, you may want to add a keyword to each reference used for a particular assignment so that you know when you search that keyword all articles related to that assignment will come up.
With your library open, select the reference you want to edit
Click on the field you would like to edit in the Reference pane to the right -OR- right-click (Cmnd+click for Mac) and select Edit References
After you finish editing the reference, click ctrl+S (Cmnd+S for Mac), or click on another reference and choose Yes when prompted to save changes